Re: swap partition leads to instability?
On Wed, 29 May 2013 19:52:02 + (UTC) jb wrote: RW rwmaillists at googlemail.com writes: BTW you mean paging, or swap use, rather that swapping. Linux supports only paging, so it can be taken as read that swapping means paging, but FreeBSD supports both. Yes, there is some confusion about the diff, if any, between paging and swapping. Paging - copying or moving pages between physical memory (RAM) and secondary storage (e.g. hard disk), in both directions. Swapping - nowdays is synonymous with paging. But its history is as follows (per Wikipedia): This is a bit Linux-centric. You say that FB supports both, Linux supports paging only. Well, Linux utilizes swap space as part of virtual memory. So, can you elaborate more on that - what is the essence of the diff, why should I avoid the term swapping when referring to Linux, assuming VMM systems on both ? You page-out pages and swap-out processes. When FreeBSD is very short of memory it swaps-out entire processes to concentrate the memory in the running processes. Linux goes directly from paging to killing processes. You can also set vm.swap_idle_enabled to allow idle processes to be swapped during normal use. This may help if a server has a lot memory tied up in processes that tend to be idle for long periods of time - traditionally used on shell servers. These days you'd probably want to be adding more memory. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap partition leads to instability?
RW rwmaillists at googlemail.com writes: ... Yes, there is some confusion about the diff, if any, between paging and swapping. Paging - copying or moving pages between physical memory (RAM) and secondary storage (e.g. hard disk), in both directions. Swapping - nowdays is synonymous with paging. But its history is as follows (per Wikipedia): This is a bit Linux-centric. ... You page-out pages and swap-out processes. When FreeBSD is very short of memory it swaps-out entire processes to concentrate the memory in the running processes. Linux goes directly from paging to killing processes. That was helpful - knowing the details of VMM implementation in various OSs helps understand the generalizations, with exceptions ... jb ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap partition leads to instability?
RW rwmaillists at googlemail.com writes: On Sun, 26 May 2013 12:36:42 + (UTC) jb wrote: But, swapping is also a symptom, not a problem. It is never a good idea to let it get to that point. No, there are thing that are better on disk than in memory. The most common example is tmpfs. It's much better that files left on tmpfs can sent to disk rather tying up physical memory indefinitely. Yup, tmpfs - in virtual memory. That's an unfortunate excuse. But before its content are swapped out, the critical system like a server will be destabilized and show lame performance. The tmp-on-tmpfs has so many disadvantages that it is difficult to count and follow all of them. jb ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap partition leads to instability?
On Sun, 26 May 2013 18:48:18 -0500 Adam Vande More wrote: Um, that is wrong. It is in fact the basically the point of TRIM. And SSD's typically use the best form of wear leveling and it's usually advisable to leave a bit of the drive unpartitioned/unused to ensure the wear leveling works optimally. Would the UFS default 8% reserve achieve that? ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap partition leads to instability?
Fred Morcos fred.morcos at gmail.com writes: .. The improvement effect can be noticed on large inputs. These algorithms will most probably perform quite badly on small inputs. I think your concern has been addressed in review of various algos where base case identification helped to avoid overhead cost in small problem sizes relative to cache. http://erikdemaine.org/papers/BRICS2002/paper.pdf In light of available but not implemented better VMM algos, perhaps *BSD and Linux could eliminate or reduce the need for: - swap space - swapping out RAM even if there is no lack of it - overcommitment of memory (a bluff asking to be punished by OOM killer) - OOM killer Besides, they allow sloppy/dangerous programming. jb ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap partition leads to instability?
On Wed, May 29, 2013 at 1:19 PM, jb jb.1234a...@gmail.com wrote: Fred Morcos fred.morcos at gmail.com writes: .. The improvement effect can be noticed on large inputs. These algorithms will most probably perform quite badly on small inputs. I think your concern has been addressed in review of various algos where base case identification helped to avoid overhead cost in small problem sizes relative to cache. http://erikdemaine.org/papers/BRICS2002/paper.pdf I will check the paper out after work, but for clarification: Also, properly written cache-oblivious algorithms tend to recursively decompose the problem until it is small enough to fit in a cache and solve each part iteratively. -- refers to the base case. The issue is when the input is small enough to be solved faster iteratively but too large to fit in the cache. Also note that this is extremely machine and cache-dependent. Still, I will check the paper out :) thanks. In light of available but not implemented better VMM algos, perhaps *BSD and Linux could eliminate or reduce the need for: - swap space I run Archlinux without any swap space on a workstation laptop without problems. I occasionally fallocate a swapfile when I need to build GHC (usually in /tmp to make use of tmpfs). - swapping out RAM even if there is no lack of it Linux has a sysctl variable vm.swappiness which you can set to 0 or 1 out of 100. Not sure how to achieve the same on FreeBSD, maybe one or more combinations of the following? vm.swap_idle_threshold2: 10 vm.swap_idle_threshold1: 2 vm.stats.vm.v_swappgsout: 236969 vm.stats.vm.v_swappgsin: 28411 vm.stats.vm.v_swapout: 92607 vm.stats.vm.v_swapin: 28285 vm.disable_swapspace_pageouts: 0 vm.defer_swapspace_pageouts: 0 vm.swap_idle_enabled: 0 - overcommitment of memory (a bluff asking to be punished by OOM killer) - OOM killer Besides, they allow sloppy/dangerous programming. jb ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap partition leads to instability?
On Sun, 26 May 2013 12:36:42 + (UTC) jb wrote: But, swapping is also a symptom, not a problem. It is never a good idea to let it get to that point. No, there are thing that are better on disk than in memory. The most common example is tmpfs. It's much better that files left on tmpfs can sent to disk rather tying up physical memory indefinitely. BTW you mean paging, or swap use, rather that swapping. Linux supports only paging, so it can be taken as read that swapping means paging, but FreeBSD supports both. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap partition leads to instability?
On Wed, 29 May 2013 13:57:22 +0200 Fred Morcos wrote: Linux has a sysctl variable vm.swappiness which you can set to 0 or 1 out of 100. Not sure how to achieve the same on FreeBSD, maybe one or more combinations of the following? You'll probably make things worse. vm.stats.vm.v_swappgsout: 236969 vm.stats.vm.v_swappgsin: 28411 vm.stats.vm.v_swapout: 92607 vm.stats.vm.v_swapin: 28285 These are just information vm.disable_swapspace_pageouts: 0 I'm not entirely sure, but I think this just disables paging at runtime - rather than compile time. vm.defer_swapspace_pageouts: 0 IIRC this defers paging, but it can end up with the paging done on the critical path rather in the background - it's usually a bad idea. vm.swap_idle_enabled: 0 vm.swap_idle_threshold2: 10 vm.swap_idle_threshold1: 2 This why you shouldn't confuse swapping and paging. These are about actually swapping-out processes. It's mainly about reducing memory use on multiuser systems where there many terminal idle at at any time. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap partition leads to instability?
On Wed, May 29, 2013 at 6:19 AM, jb jb.1234a...@gmail.com wrote: - overcommitment of memory (a bluff asking to be punished by OOM killer) No self respecting Unix has an OOM by default. - OOM killer Are you suggesting FreeBSD does this crap? Besides, they allow sloppy/dangerous programming. Yup, in the kernel. -- Adam Vande More ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap partition leads to instability?
On Sun, May 26, 2013 at 6:17 PM, Adam Vande More amvandem...@gmail.comwrote: Normal dynamic wear leveling on a modern SSD will be better than imposing an FS- backed swap for 4GB partion occupying a small fraction of total drive space. Quite so. - M ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap partition leads to instability?
On Wed, 29 May 2013, Michael Sierchio wrote: On Sun, May 26, 2013 at 6:17 PM, Adam Vande More amvandem...@gmail.com wrote: Normal dynamic wear leveling on a modern SSD will be better than imposing an FS- backed swap for 4GB partion occupying a small fraction of total drive space. And you don't think the presence of TRIM--where the SSD can actually know which blocks are no longer in use--is worthwhile? ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap partition leads to instability?
On Wed, May 29, 2013 at 1:05 PM, Warren Block wbl...@wonkity.com wrote: And you don't think the presence of TRIM--where the SSD can actually know which blocks are no longer in use--is worthwhile? As a whole, TRIM is worthwhile. However when an SSD is overprovisioned it provides a lot of benefits. TRIM-less swap in this case doesn't. The PE rate of the worst MLC SSD's at this point is @3000 AFAIK. Given those figures and average desktop swap rate at my estimation, prioritizing write endurance on an SSD is not beneficial(especially with a SanForce). If you are swapping continuously something like ZeusRAM may be required. There are probably other solutions available as well as other 3rd party ones. If you are swapping a lot, the best case is usually to add RAM. -- Adam Vande More ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap partition leads to instability?
PS -- Moderating questions@ is just awful. I'm disappointed. On Wed, May 29, 2013 at 1:34 PM, Adam Vande More amvandem...@gmail.com wrote: On Wed, May 29, 2013 at 1:05 PM, Warren Block wbl...@wonkity.com wrote: And you don't think the presence of TRIM--where the SSD can actually know which blocks are no longer in use--is worthwhile? As a whole, TRIM is worthwhile. However when an SSD is overprovisioned it provides a lot of benefits. TRIM-less swap in this case doesn't. The PE rate of the worst MLC SSD's at this point is @3000 AFAIK. Given those figures and average desktop swap rate at my estimation, prioritizing write endurance on an SSD is not beneficial(especially with a SanForce). If you are swapping continuously something like ZeusRAM may be required. There are probably other solutions available as well as other 3rd party ones. If you are swapping a lot, the best case is usually to add RAM. -- Adam Vande More -- Adam Vande More ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap partition leads to instability?
RW rwmaillists at googlemail.com writes: On Sun, 26 May 2013 12:36:42 + (UTC) jb wrote: But, swapping is also a symptom, not a problem. It is never a good idea to let it get to that point. No, there are thing that are better on disk than in memory. The most common example is tmpfs. It's much better that files left on tmpfs can sent to disk rather tying up physical memory indefinitely. BTW you mean paging, or swap use, rather that swapping. Linux supports only paging, so it can be taken as read that swapping means paging, but FreeBSD supports both. Yes, there is some confusion about the diff, if any, between paging and swapping. Paging - copying or moving pages between physical memory (RAM) and secondary storage (e.g. hard disk), in both directions. Swapping - nowdays is synonymous with paging. But its history is as follows (per Wikipedia): Historically, swapping referred to moving from/to secondary storage a whole program at a time, in a scheme known as roll-in/roll-out. In the 1960s, after the concept of virtual memory was introduced — in two variants, either using segments or pages — the term swapping was applied to moving, respectively, either segments or pages, between memory and disk. Today with the virtual memory mostly based on pages, not segments, swapping became a fairly close synonym of paging. You say that FB supports both, Linux supports paging only. Well, Linux utilizes swap space as part of virtual memory. So, can you elaborate more on that - what is the essence of the diff, why should I avoid the term swapping when referring to Linux, assuming VMM systems on both ? jb ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap partition leads to instability?
On Wed, May 29, 2013 at 2:52 PM, jb jb.1234a...@gmail.com wrote: Well, Linux utilizes swap space as part of virtual memory. As does every other Unix. -- Adam Vande More ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap partition leads to instability?
On May 29, 2013, at 3:52 PM, jb jb.1234a...@gmail.com wrote: Yes, there is some confusion about the diff, if any, between paging and swapping. Paging - copying or moving pages between physical memory (RAM) and secondary storage (e.g. hard disk), in both directions. Swapping - nowdays is synonymous with paging. You say that FB supports both, Linux supports paging only. Well, Linux utilizes swap space as part of virtual memory. So, can you elaborate more on that - what is the essence of the diff, why should I avoid the term swapping when referring to Linux, assuming VMM systems on both ? When I started working professionally with Unix systems in 1995, I was taught that paging was the process of copying least used pages of RAM onto disk so that the RAM could be freed if the system needed more RAM. Swapping was the process of moving an entire program from RAM to disk in order to free up RAM. In other words, a process can be swapped out and placed on disk until it comes up to run again, at which point it can be swapped in and executed. I think that much of the confusion comes from the use of the SWAP device by the PAGING system. When the concept of paging came about, it just used the already existing SWAP space to store it's paged out pages of memory. On the systems I worked on at the time (SunOS / Solaris), paging was a sign of pressure on the physical memory (RAM) of a system, swapping was a sign of _severe_ physical memory pressure. This was a time when we configured 2 to 4 times the amount of physical RAM as SWAP space. RAM was very expensive and hard drives just expensive :-) It was common on a normally operating system to see the page scanner* running up to 100 times per second. A scan rate of over 100 was considered a sign of pressure on RAM that needed to be addressed, any SWAPing was considered a sign that the system needed more physical RAM. Today RAM is so cheap that _any_ paging is often considered bad and an indication that more Ram should be added. *Solaris Page Scanner: This is a kernel level process that wakes up, examines the amount of free RAM, and takes action based on that value. The thresholds are all dynamic and based on the amount of RAM in the system. Above a high water mark the scanner does nothing. As the amount of free RAM drops, various pages of RAM are copied to SWAP space and the RAM freed. Eventually, if the amount of free Ram falls low enough, even parts of the kernel will be paged out. This is very bad and can lead to a system thrashing where it spends the vast majority of it's time just paging in and out and not actually getting anything done. -- Paul Kraus Deputy Technical Director, LoneStarCon 3 Sound Coordinator, Schenectady Light Opera Company ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap partition leads to instability?
Follow up comment. It has been pointed out to me that there is Varnish software taking advantage of system VMM and swap space. Well, there are cache-oblivious algorithms that perform as well, and so they make the above (disk access model; cache-aware model) unnecessary (obsolete ?) and are superior in their generality. jb ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap partition leads to instability?
On Tue, May 28, 2013 at 8:42 PM, jb jb.1234a...@gmail.com wrote: Follow up comment. It has been pointed out to me that there is Varnish software taking advantage of system VMM and swap space. Well, there are cache-oblivious algorithms that perform as well, and so they make the above (disk access model; cache-aware model) unnecessary (obsolete ?) and are superior in their generality. Note that such cache-oblivious algorithms cannot be trivially applied to any problem. Also, properly written cache-oblivious algorithms tend to recursively decompose the problem until it is small enough to fit in a cache and solve each part iteratively. The improvement effect can be noticed on large inputs. These algorithms will most probably perform quite badly on small inputs. jb ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap partition leads to instability?
On 26. mai 2013, at 10:58, M. V. bored_to_deat...@yahoo.com wrote: But recently I heard from a FreeBSD expert that I shouldn't have swap partition for my server, and having swap partition could make my server unstable Any chance this could be a simple misunderstanding? That he objected to the thought of the server swapping on an SSD (or whereever), more than the idea of having the partition itself? If you're heavily swapping on an SSD with no redundancy, sooner or later it will kill your server. Generally though, havin too little memory will also give issues. ;) I usually recommend viewing swap like you view filesystems. If you don't want downtime or dataloss when it dies, plan for failiure, and use gmirror or zfs mirror and zvol. Terje ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap partition leads to instability?
jb jb.1234abcd at gmail.com writes: M. V. bored_to_death85 at yahoo.com writes: recently I heard from a FreeBSD expert that I shouldn't have swap partition for my server, and having swap partition could make my server unstable. I think your FB expert was up to something. I bet he spoke out of experience. Swapping by itself can decrease system reliability due to possible data corruption on swap disk or during two-way transfers, with subsequent incorrect RAM and machine crash. But, swapping is also a symptom, not a problem. It is never a good idea to let it get to that point. ... http://blog.jcole.us/2010/09/28/mysql-swap-insanity-and-the-numa-architecture/ Very interesting point. - do you think this could hurt my server's stability too? (most of its work is a noticeable amount of packet-forwarding, and other network services, like firewall, dhcp server, ntp server, etc) - if so, in what conditions? can I do something to prevent this? or should I just get rid of the swap partition? - does swap partition do any good for me at all? I mean if we even suppose nothing bad happens because of it, is it worth risking to keep it? thank you. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap partition leads to instability?
Hi, On Sun, 26 May 2013 01:58:32 -0700 (PDT) M. V. bored_to_deat...@yahoo.com wrote: I have a 24/7 network server/gateway with FreeBSD-8.2 on a SSD drive. it's partitioned as normal (/ , /tmp, /var , /usr and swap) for a long time now. But recently I heard from a FreeBSD expert that I shouldn't have swap partition for my server, and having swap partition could make my server unstable. this was so strange for me, and I searched a lot but couldn't find a reason for this claim. because it is a false claim. I never ever have had any system with working hard, that gave a problem because of the swap space. Erich ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap partition leads to instability?
On Sun, 26 May 2013 16:09:06 +0700, Erich Dollansky wrote: Hi, On Sun, 26 May 2013 01:58:32 -0700 (PDT) M. V. bored_to_deat...@yahoo.com wrote: I have a 24/7 network server/gateway with FreeBSD-8.2 on a SSD drive. it's partitioned as normal (/ , /tmp, /var , /usr and swap) for a long time now. But recently I heard from a FreeBSD expert that I shouldn't have swap partition for my server, and having swap partition could make my server unstable. this was so strange for me, and I searched a lot but couldn't find a reason for this claim. because it is a false claim. I never ever have had any system with working hard, that gave a problem because of the swap space. I think the problem here is that he's using a SSD. As soon as the swap partition is being in heavy use, which means it receives many writes, this may lead to the SSD wearing out, decreasing its lifetime. Swap space usually does not make a system unstable. Sometimes, the opposite is true. :-) So if you're using a SSD, you can apply certain optimizations to increase its lifetime so it can be in use for several years (running 24/7). Here are some suggestions -- check if they are useful in your specific case! # newfs -m 0 -i 16384 -b 16384 -f 2048 -U /dev/ada0a This assumes that you don't have created any slices, just one bootable partition covering the whole disk (therefor ada0a). Create a swapfile like this: # /bin/rm -f /swapfile.tmp # /bin/dd if=/dev/zero of=/swapfile.tmp bs=16m seek=1k count=0 # /sbin/mdconfig -a -t vnode -u 0 -f /swapfile.tmp || /bin/sh # /bin/chflags nodump /swapfile.tmp # /bin/rm -f /swapfile.tmp # /sbin/swapctl -a /dev/md0 This makes the system use a disk-backed dynamic swap file. If the swap won't be used, no space will be occupied or reserved on the SSD. You can also think about changing stuff you won't need to store on the SSD, maybe some content of /tmp or /var. You can also put those into a memory disk. The SSD rule is: Minimize writes if you can. This is a _general_ rule and does not correspond to swap only! -- Polytropon Magdeburg, Germany Happy FreeBSD user since 4.0 Andra moi ennepe, Mousa, ... ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap partition leads to instability?
On Sun, 26 May 2013 01:58:32 -0700 (PDT) M. V. bored_to_deat...@yahoo.com wrote: hi everyone, I have a 24/7 network server/gateway with FreeBSD-8.2 on a SSD drive. it's partitioned as normal (/ , /tmp, /var , /usr and swap) for a long time now. But recently I heard from a FreeBSD expert that I shouldn't have swap partition for my server, and having swap partition could make my server unstable. this was so strange for me, and I searched a lot but couldn't find a reason for this claim. so my question is simple: - could having a swap partition, be a bad thing for my FreeBSD server? and if so, why and in what conditions? I never had a problem with swap partitions, but perhaps the FreeBSD expert may refer to one of this three issues I can think about problems with swap, none of them are unstability issues: a) Swap partitions may store info from previous boot, you can use swap encryption for that. b) When using swap files (mounting a swap in a file), at shutdown sometimes there's a race condition and swap is unmounted before it's empty. c) If your system needs to use swap, network apps may show/throw timeouts when swap i/o is heavy. Sometimes b) kicks me but it's my fault because i don't shutdown process properly. Cheers! L --- --- Eduardo Morras emorr...@yahoo.es ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap partition leads to instability?
Hi, sorry for my English. Here is what I wanted to say. On Sun, 26 May 2013 16:09:06 +0700 Erich Dollansky erichsfreebsdl...@alogt.com wrote: Hi, On Sun, 26 May 2013 01:58:32 -0700 (PDT) M. V. bored_to_deat...@yahoo.com wrote: I have a 24/7 network server/gateway with FreeBSD-8.2 on a SSD drive. it's partitioned as normal (/ , /tmp, /var , /usr and swap) for a long time now. But recently I heard from a FreeBSD expert that I shouldn't have swap partition for my server, and having swap partition could make my server unstable. this was so strange for me, and I searched a lot but couldn't find a reason for this claim. because it is a false claim. I never ever have had any system with working hard, that gave a problem because of the swap space. I never ever have had any system which was working hard that gave problems because of the swaps space. Erich Erich ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap partition leads to instability?
On 26/05/2013 09:58, M. V. wrote: hi everyone, I have a 24/7 network server/gateway with FreeBSD-8.2 on a SSD drive. it's partitioned as normal (/ , /tmp, /var , /usr and swap) for a long time now. But recently I heard from a FreeBSD expert that I shouldn't have swap partition for my server, and having swap partition could make my server unstable. this was so strange for me, and I searched a lot but couldn't find a reason for this claim. so my question is simple: - could having a swap partition, be a bad thing for my FreeBSD server? and if so, why and in what conditions? Having a swap partition is absolutely standard for server or workstation class machines, and should be implemented as a matter of course. Even if the machine has much more memory than it would generally ever use and so have no actual need to swap. About the only circumstances where you wouldn't want swap is if you were creating an embedded appliance and eg. didn't have any writable disk space. That's pretty extraordinary and as such a system would have to be heavily customized over stock FreeBSD anyhow, so not having swap would fade into insignificance compared to the other changes that would be required. Why is swap needed? Nowadays, memory is sufficiently cheap and system boards are capable of loading so much of it, that the only sensible strategy is to have more physical RAM than is required to keep your normal application load working. So a swap partition should not be routinely involved in swapping memory pages back and forth. Even so, idle pages can be swapped out -- there's no point in having an unreferenced memory page sitting in RAM taking up space that could be used productively by an active process. A small amount of swap usage like this is standard. A large amount of swap usage like this indicates you need to switch to using better written software. Swap is also useful to buffer against unexpected spikes in memory usage. Sure, performance generally nosedives once a system starts actively swapping, but that may be a better outcome than the alternative if there is no swap capacity available: which is for the kernel to start killing off processes in an attempt to reduce memory pressure. Finally, swap is used as the place to record kernel state in the event of system crashes. You could use any otherwise unused disk partition for that, but swap is traditional. This is where the hoary old recipe of 'swap = twice ram' came from, although nowadays what with minidumps and the generally larger amounts of RAM in use you don't need to provide anything like as much as that. If you're bothered by having a few GiB of disk allocated as swap but basically idle, then look into tmpfs or mdmfs for /tmp -- that will let you make productive use the space while still keeping the ability to save crashdumps if needed. Some caveats about where to put a swap area: * If your system is under memory pressure, then your swap area can be extremely active. In these circumstances putting swap on a SSD card or other device with a limited number of write-cycles is not a good choice. * If you are using ZFS, and again, if you are under memory pressure, then putting swap on a ZFS can lead to a deadlock where the system needs to allocate more memory to deal with an out-of-memory condition. In this case, it is recommended to create a separate swap partition not managed by ZFS. Otherwise, swap can go anywhere. A dedicated partition will give better performance than swapping to a file, but file-backed swap is handy if you need to add swap in a hurry. For resilience, mirror swap partitions in pairs -- gmirror(8) is a good tool for that. Don't try using any of the higher RAID levels for swap areas -- their performance characteristics are not a good match to the sort of IO a swap area does. For best performance, you should spread swap areas over as many disk spindles as possible. You can create numerous swap areas and the system will automatically stripe any IO across them. Cheers, Matthew -- Dr Matthew J Seaman MA, D.Phil. PGP: http://www.infracaninophile.co.uk/pgpkey signature.asc Description: OpenPGP digital signature
Re: swap partition leads to instability?
M. V. bored_to_death85 at yahoo.com writes: hi everyone, I have a 24/7 network server/gateway with FreeBSD-8.2 on a SSD drive. it's partitioned as normal (/ , /tmp, /var , /usr and swap) for a long time now. But recently I heard from a FreeBSD expert that I shouldn't have swap partition for my server, and having swap partition could make my server unstable. this was so strange for me, and I searched a lot but couldn't find a reason for this claim. so my question is simple: - could having a swap partition, be a bad thing for my FreeBSD server? and if so, why and in what conditions? Cheers! Hi, I think your FB expert was up to something. I bet he spoke out of experience. Swapping by itself can decrease system reliability due to possible data corruption on swap disk or during two-way transfers, with subsequent incorrect RAM and machine crash. But, swapping is also a symptom, not a problem. It is never a good idea to let it get to that point. Badly written, architected, or tuned server app or system are the reason. Think of RDBMS/SQL server processing real-time on-line transactions and how much it goes into setting it up properly for a heavy use. On a smaller scale, consider this example: http://blog.jcole.us/2010/09/28/mysql-swap-insanity-and-the-numa-architecture/ jb ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap partition leads to instability?
The Intel SLC mSATA drives I use in embedded devices don't support TRIM, but - it doesn't seem to matter. Actually, I'm confident that just using bare partitions for swap is fine, and I haven't had any of the trouble I witnessed with MLC devices. The difference is that the size is limited to under 32GB. - M On Sun, May 26, 2013 at 4:32 PM, Warren Block wbl...@wonkity.com wrote: On Sun, 26 May 2013, Polytropon wrote: On Sun, 26 May 2013 16:09:06 +0700, Erich Dollansky wrote: Hi, On Sun, 26 May 2013 01:58:32 -0700 (PDT) M. V. bored_to_deat...@yahoo.com wrote: I have a 24/7 network server/gateway with FreeBSD-8.2 on a SSD drive. it's partitioned as normal (/ , /tmp, /var , /usr and swap) for a long time now. But recently I heard from a FreeBSD expert that I shouldn't have swap partition for my server, and having swap partition could make my server unstable. this was so strange for me, and I searched a lot but couldn't find a reason for this claim. because it is a false claim. I never ever have had any system with working hard, that gave a problem because of the swap space. I think the problem here is that he's using a SSD. As soon as the swap partition is being in heavy use, which means it receives many writes, this may lead to the SSD wearing out, decreasing its lifetime. Another problem with SSDs is that they can have difficulty with wear leveling. This is even worse with swap because there is no way to use TRIM to tell the SSD about blocks that have been freed. The workaround is a swapfile on UFS with TRIM enabled. It works fine, and even better when you update the rc scripts for shutdown. Here's an article on setup: http://www.wonkity.com/~**wblock/docs/html/ssd.htmlhttp://www.wonkity.com/~wblock/docs/html/ssd.html And here is the PR with a patch: http://www.freebsd.org/cgi/**query-pr.cgi?pr=bin/168544http://www.freebsd.org/cgi/query-pr.cgi?pr=bin/168544 __**_ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/**mailman/listinfo/freebsd-**questionshttp://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-** unsubscr...@freebsd.org freebsd-questions-unsubscr...@freebsd.org ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap partition leads to instability?
On Sun, 26 May 2013, Polytropon wrote: On Sun, 26 May 2013 16:09:06 +0700, Erich Dollansky wrote: Hi, On Sun, 26 May 2013 01:58:32 -0700 (PDT) M. V. bored_to_deat...@yahoo.com wrote: I have a 24/7 network server/gateway with FreeBSD-8.2 on a SSD drive. it's partitioned as normal (/ , /tmp, /var , /usr and swap) for a long time now. But recently I heard from a FreeBSD expert that I shouldn't have swap partition for my server, and having swap partition could make my server unstable. this was so strange for me, and I searched a lot but couldn't find a reason for this claim. because it is a false claim. I never ever have had any system with working hard, that gave a problem because of the swap space. I think the problem here is that he's using a SSD. As soon as the swap partition is being in heavy use, which means it receives many writes, this may lead to the SSD wearing out, decreasing its lifetime. Another problem with SSDs is that they can have difficulty with wear leveling. This is even worse with swap because there is no way to use TRIM to tell the SSD about blocks that have been freed. The workaround is a swapfile on UFS with TRIM enabled. It works fine, and even better when you update the rc scripts for shutdown. Here's an article on setup: http://www.wonkity.com/~wblock/docs/html/ssd.html And here is the PR with a patch: http://www.freebsd.org/cgi/query-pr.cgi?pr=bin/168544 ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap partition leads to instability?
On Sun, May 26, 2013 at 6:32 PM, Warren Block wbl...@wonkity.com wrote: Another problem with SSDs is that they can have difficulty with wear leveling. This is even worse with swap because there is no way to use TRIM to tell the SSD about blocks that have been freed. Um, that is wrong. It is in fact the basically the point of TRIM. And SSD's typically use the best form of wear leveling and it's usually advisable to leave a bit of the drive unpartitioned/unused to ensure the wear leveling works optimally. -- Adam Vande More ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap partition leads to instability?
On Sun, 26 May 2013, Adam Vande More wrote: On Sun, May 26, 2013 at 6:32 PM, Warren Block wbl...@wonkity.com wrote: Another problem with SSDs is that they can have difficulty with wear leveling. This is even worse with swap because there is no way to use TRIM to tell the SSD about blocks that have been freed. Um, that is wrong. Which part? A FreeBSD swap partition has no way to use TRIM, so I suggest using a swap file on top of UFS, which does support TRIM. It is in fact the basically the point of TRIM. And SSD's typically use the best form of wear leveling and it's usually advisable to leave a bit of the drive unpartitioned/unused to ensure the wear leveling works optimally. Using TRIM should preserve performance better than leaving unused space and letting the drive wear leveling algorithm move data around without the hint. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap partition leads to instability?
On Sun, May 26, 2013 at 7:20 PM, Warren Block wbl...@wonkity.com wrote: Which part? This part: Another problem with SSDs is that they can have difficulty with wear leveling. Do as I suggested and you'll get maximum life from the drive even with swap present. Even absent of best practices, SSD's in general do a great job in managing wear leveling. We're 5+ years out from crappy SSD's with dynamic wear leveling. Modern SSD's don't suffer nearly the write amplification effect of earlier drives. Also the write amplification effect only comes into play during random writes. A lot of common swap usage isn't random. All this is of course assuming we're dealing with a quality drive. If you're using a cheap Chinese knock off, all bets are off. A FreeBSD swap partition has no way to use TRIM, so I suggest using a swap file on top of UFS, which does support TRIM. Using TRIM should preserve performance better than leaving unused space and letting the drive wear leveling algorithm move data around without the hint. Normal dynamic wear leveling on a modern SSD will be better than imposing an FS- backed swap for 4GB partion occupying a small fraction of total drive space. File backed paging imposes two sets of bottlenecks and TRIM only *helps* with one. Another part of the equation is how much is swap used. If rarely, this is a non-issue to begin with. If it's significant, any flash SSD probably isn't appropriate. Certain other SSD's are not subject to these guidelines at all. -- Adam Vande More ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Swap files and panics
At 10:54 AM 5/29/2012, Warren Block wrote: Recently I rearranged partitions on an SSD. The swap partition was eliminated in favor of a swap file on /usr. This works, allows TRIM support on the swap space, and is easier to resize than a partition. However, sometimes the system panics on shutdown. It happens after syncing disks, so the filesystems are fine, but it's disconcerting. I suspect but haven't yet managed to prove that it's only when swap is not empty. A race condition involving when the filesystems are unmounted? Or should there be some code in /etc/rc.d/addswap to run swapoff before shutdown? This is on a very recent 9-STABLE amd64, i5 2500K. rc.conf: swapfile=/usr/swap/swap Did you remove the old swap file entry from /etc/fstab? -Derek -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap space
On 2/17/2012 6:54 PM, Jim Pazarena wrote: is there a command which can show the size of the hard drive swap? % pstat -T 438/12328 files 98M/10240M swap space ---Mike -- --- Mike Tancsa, tel +1 519 651 3400 Sentex Communications, m...@sentex.net Providing Internet services since 1994 www.sentex.net Cambridge, Ontario Canada http://www.tancsa.com/ ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap space
On Feb 17, 2012, at 3:54 PM, Jim Pazarena wrote: is there a command which can show the size of the hard drive swap? A df seems to avoid the swap area. You're looking for swapinfo Regards, -- -Chuck ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap space
On Feb 17, 2012 6:55 PM, Jim Pazarena fqu...@paz.bz wrote: is there a command which can show the size of the hard drive swap? A df seems to avoid the swap area. This would be on a live production server. Thanks. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org Top or vmstat ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap space
On 02/17/2012 15:58, Chuck Swiger wrote: On Feb 17, 2012, at 3:54 PM, Jim Pazarena wrote: is there a command which can show the size of the hard drive swap? A df seems to avoid the swap area. You're looking for swapinfo Regards, Chuck beat me to it. swapinfo or top are the two ways I normally check. -- Dave Robison Sales Solution Architect II FIS Banking Solutions 510/621-2089 (w) 530/518-5194 (c) 510/621-2020 (f) da...@vicor.com david.robi...@fisglobal.com _ The information contained in this message is proprietary and/or confidential. If you are not the intended recipient, please: (i) delete the message and all copies; (ii) do not disclose, distribute or use the message in any manner; and (iii) notify the sender immediately. In addition, please be aware that any message addressed to our domain is subject to archiving and review by persons other than the intended recipient. Thank you. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
RE: swap space
-Original Message- From: owner-freebsd-questi...@freebsd.org [mailto:owner-freebsd- questi...@freebsd.org] On Behalf Of Robison, Dave Sent: Friday, February 17, 2012 4:11 PM To: freebsd-questions@freebsd.org Subject: Re: swap space On 02/17/2012 15:58, Chuck Swiger wrote: On Feb 17, 2012, at 3:54 PM, Jim Pazarena wrote: is there a command which can show the size of the hard drive swap? A df seems to avoid the swap area. You're looking for swapinfo Regards, Chuck beat me to it. swapinfo or top are the two ways I normally check. I'm digging the fact that it now accepts -h to produce human-readable sizes. swapinfo didn't always support -h -- Devin _ The information contained in this message is proprietary and/or confidential. If you are not the intended recipient, please: (i) delete the message and all copies; (ii) do not disclose, distribute or use the message in any manner; and (iii) notify the sender immediately. In addition, please be aware that any message addressed to our domain is subject to archiving and review by persons other than the intended recipient. Thank you. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap space
From owner-freebsd-questi...@freebsd.org Fri Feb 17 17:59:50 2012 Date: Fri, 17 Feb 2012 15:54:18 -0800 From: Jim Pazarena fqu...@paz.bz To: FreeBSD Mailing List freebsd-questions@freebsd.org Subject: swap space is there a command which can show the size of the hard drive swap? A df seems to avoid the swap area. That *is* expected behavior. 'df' shows utilization of -filesystems-. 'swap' is not filesystem. This would be on a live production server. The traditional means is 'pstat -s'. On relatively modern systems, 'swapinfo' is an alias. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Swap Space
On 05/01/2011 22:33, Jeff Whitman wrote: I'm finding conflicting data on this. Some say 0, some say 1 times RAM, others say stay with 2 x RAM. Standard advice is 2x RAM -- but that dates back to the days when servers would have quantities of RAM measured in Megabytes rather than Gigabytes. 2 X RAM is a lot of disk space nowadays -- so either you'll need to find some other use for that space; eg. as a swap-backed /tmp partition, or else provide less swap. Also, there's a maximum of -- I think -- 8GB swap above which the performance of swap is degraded, due to algorithmic limits in the way memory pages are mapped onto disk pages. You need 1 x RAM + a few kB in order to support getting a crashdump. Or at least, you did before the days of minidumps. Not sure what the requirements are for getting system dumps nowadays. Swap space used for crashdumps should be a raw partition, not a file. On the other hand, for good performance you should not be using any significant amounts of swap in normal usage. You will need some swap, as the OS tends to use a small amount even when not under memory pressure. You should have swap to act as a buffer in case your machine suddenly starts using up more memory than you expect, either because of memory leaks, or due to demand spikes or through any number of other possible causes. Therefore, I think the best advice for a modern large memory system would be: If RAM 8GB, then SWAP = 8GB[*] If RAM 8GB, then SWAP = 1 x RAM + delta where delta is perhaps a Megabyte or so. Just rounding the partition size up to the next cylinder boundary should be enough (which happens automatically with most partitioning schemes). Cheers, Matthew [*] In this case, if you need crashdumps, you should dedicate another otherwise unused partition of the correct size as your dumpdev. -- Dr Matthew J Seaman MA, D.Phil. 7 Priory Courtyard Flat 3 PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate JID: matt...@infracaninophile.co.uk Kent, CT11 9PW signature.asc Description: OpenPGP digital signature
Re: Swap Space
On Thu, Jan 06, 2011 at 09:42:36AM +, Matthew Seaman wrote: On 05/01/2011 22:33, Jeff Whitman wrote: I'm finding conflicting data on this. Some say 0, some say 1 times RAM, others say stay with 2 x RAM. Standard advice is 2x RAM -- but that dates back to the days when servers would have quantities of RAM measured in Megabytes rather than Gigabytes. Of course, in those days disk space was measured in MBytes too. Also, there's a maximum of -- I think -- 8GB swap above which the performance of swap is degraded, due to algorithmic limits in the way memory pages are mapped onto disk pages. I don't know about an 8GB limit for swap performance. I suppose it is possible.So, the following formula from Mathew is probably a good new rule of thumb. You need 1 x RAM + a few kB in order to support getting a crashdump. Or at least, you did before the days of minidumps. Not sure what the requirements are for getting system dumps nowadays. Swap space used for crashdumps should be a raw partition, not a file. jerry On the other hand, for good performance you should not be using any significant amounts of swap in normal usage. You will need some swap, as the OS tends to use a small amount even when not under memory pressure. You should have swap to act as a buffer in case your machine suddenly starts using up more memory than you expect, either because of memory leaks, or due to demand spikes or through any number of other possible causes. Therefore, I think the best advice for a modern large memory system would be: If RAM 8GB, then SWAP = 8GB[*] If RAM 8GB, then SWAP = 1 x RAM + delta where delta is perhaps a Megabyte or so. Just rounding the partition size up to the next cylinder boundary should be enough (which happens automatically with most partitioning schemes). Cheers, Matthew [*] In this case, if you need crashdumps, you should dedicate another otherwise unused partition of the correct size as your dumpdev. -- Dr Matthew J Seaman MA, D.Phil. 7 Priory Courtyard Flat 3 PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate JID: matt...@infracaninophile.co.uk Kent, CT11 9PW ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Swap Space
On Wed, Jan 5, 2011 at 4:33 PM, Jeff Whitman jwhit...@jwnetsource.comwrote: I will be installing 8.1 on a Dell Poweredge 2850, with dual 3 GHz XEON processors and 6GB RAM. What is the recommended swap space? I'm finding conflicting data on this. Some say 0, some say 1 times RAM, others say stay with 2 x RAM. Definitely not 0, but 2x would probably be way too much IMO. 4 - 6 GB should be enough for most use cases. -- Adam Vande More ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
RE: Swap Space
I will be installing 8.1 on a Dell Poweredge 2850, with dual 3 GHz XEON processors and 6GB RAM. What is the recommended swap space? I'm finding conflicting data on this. Some say 0, some say 1 times RAM, others say stay with 2 x RAM. Definitely not 0, but 2x would probably be way too much IMO. 4 - 6 GB should be enough for most use cases. Correct me if I'm wrong, but if necessary one could add (and activate) a secondary / additional swap file if necessary without rebooting. So maybe start with a few gig and add an additional swap file if necessary? font size=1 div style='border:none;border-bottom:double windowtext 2.25pt;padding:0in 0in 1.0pt 0in' /div This email is intended to be reviewed by only the intended recipient and may contain information that is privileged and/or confidential. If you are not the intended recipient, you are hereby notified that any review, use, dissemination, disclosure or copying of this email and its attachments, if any, is strictly prohibited. If you have received this email in error, please immediately notify the sender by return email and delete this email from your system. /font ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Swap Space
On Wed, 5 Jan 2011 17:20:48 -0600 Gary Gatten ggat...@waddell.com wrote: Correct me if I'm wrong, but if necessary one could add (and activate) a secondary / additional swap file if necessary without rebooting. So maybe start with a few gig and add an additional swap file if necessary? Swapping to a file is really slow and should only be done if absolutely necessary since every read/write has to go through the filesystem code which it doesn't do if done via a swap slice. -- Bruce Cran ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
RE: Swap Space
Correct me if I'm wrong, but if necessary one could add (and activate) a secondary / additional swap file if necessary without rebooting. So maybe start with a few gig and add an additional swap file if necessary? Swapping to a file is really slow and should only be done if absolutely necessary since every read/write has to go through the filesystem code which it doesn't do if done via a swap slice. Good point. It's been several years and back on v5 or 6 when I did something like this. If there's unpartitioned space on the drive, can one add a secondary swap partition real-time? I forget what I did here - I'm sure I followed what's in the handbook re swap space. Probably did a swap file... font size=1 div style='border:none;border-bottom:double windowtext 2.25pt;padding:0in 0in 1.0pt 0in' /div This email is intended to be reviewed by only the intended recipient and may contain information that is privileged and/or confidential. If you are not the intended recipient, you are hereby notified that any review, use, dissemination, disclosure or copying of this email and its attachments, if any, is strictly prohibited. If you have received this email in error, please immediately notify the sender by return email and delete this email from your system. /font ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Swap Space
On Wed, Jan 5, 2011 at 5:33 PM, Gary Gatten ggat...@waddell.com wrote: Correct me if I'm wrong, but if necessary one could add (and activate) a secondary / additional swap file if necessary without rebooting. So maybe start with a few gig and add an additional swap file if necessary? Swapping to a file is really slow and should only be done if absolutely necessary since every read/write has to go through the filesystem code which it doesn't do if done via a swap slice. Good point. It's been several years and back on v5 or 6 when I did something like this. If there's unpartitioned space on the drive, can one add a secondary swap partition real-time? I forget what I did here - I'm sure I followed what's in the handbook re swap space. Probably did a swap file... Yes you can do that with swapon(1) It's been said though that FreeBSD memory paging algorithms take into account the system's entire available VM for deciding on when to act in low memory conditions and these parameters are tuned expect some of that to be swap space. That is why one reason there *should* be a least some swap space even on a system w/ plenty of RAM. -- Adam Vande More ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
RE: Swap Space - hijack?
Correct me if I'm wrong, but if necessary one could add (and activate) a secondary / additional swap file if necessary without rebooting. So maybe start with a few gig and add an additional swap file if necessary? Swapping to a file is really slow and should only be done if absolutely necessary since every read/write has to go through the filesystem code which it doesn't do if done via a swap slice. Good point. It's been several years and back on v5 or 6 when I did something like this. If there's unpartitioned space on the drive, can one add a secondary swap partition real-time? I forget what I did here - I'm sure I followed what's in the handbook re swap space. Probably did a swap file... Yes you can do that with swapon(1) It's been said though that FreeBSD memory paging algorithms take into account the system's entire available VM for deciding on when to act in low memory conditions and these parameters are tuned expect some of that to be swap space. That is why one reason there *should* be a least some swap space even on a system w/ plenty of RAM. Sorry for the probable hijack... Speaking of swapping algorithms, is there a way to force a parent and all child processes to NOT be swapped - period - and always remain 100% in real memory? And if so, is it discouraged or completely up to the sysadmin? font size=1 div style='border:none;border-bottom:double windowtext 2.25pt;padding:0in 0in 1.0pt 0in' /div This email is intended to be reviewed by only the intended recipient and may contain information that is privileged and/or confidential. If you are not the intended recipient, you are hereby notified that any review, use, dissemination, disclosure or copying of this email and its attachments, if any, is strictly prohibited. If you have received this email in error, please immediately notify the sender by return email and delete this email from your system. /font ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Swap Space
Adam Vande More writes: I will be installing 8.1 on a Dell Poweredge 2850, with dual 3 GHz XEON processors and 6GB RAM. What is the recommended swap space? I'm finding conflicting data on this. Some say 0, some say 1 times RAM, others say stay with 2 x RAM. Definitely not 0, but 2x would probably be way too much IMO. 4 - 6 GB should be enough for most use cases. One data point: last pid: 58457; load averages: 1.91, 2.20, 2.27 up 8+19:16:27 18:51:23 166 processes: 5 running, 158 sleeping, 2 stopped, 1 zombie Mem: 1541M Active, 1267M Inact, 1223M Wired, 195M Cache, 802M Buf, 3440M Free Swap: 18G Total, 11M Used, 18G Free (That's 8g total memory.) It's a fairly lightly loaded workstation. A philosophical consideration: modern disks are cheap, and fairly fast. Repartitioning if you don't have enough is a pain. Robert Huff ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Swap Space
On 01/05/11 15:20, Gary Gatten wrote: I will be installing 8.1 on a Dell Poweredge 2850, with dual 3 GHz XEON processors and 6GB RAM. What is the recommended swap space? I'm finding conflicting data on this. Some say 0, some say 1 times RAM, others say stay with 2 x RAM. Definitely not 0, but 2x would probably be way too much IMO. 4 - 6 GB should be enough for most use cases. Correct me if I'm wrong, but if necessary one could add (and activate) a secondary / additional swap file if necessary without rebooting. So maybe start with a few gig and add an additional swap file if necessary? font size=1 div style='border:none;border-bottom:double windowtext 2.25pt;padding:0in 0in 1.0pt 0in' /div This email is intended to be reviewed by only the intended recipient and may contain information that is privileged and/or confidential. If you are not the intended recipient, you are hereby notified that any review, use, dissemination, disclosure or copying of this email and its attachments, if any, is strictly prohibited. If you have received this email in error, please immediately notify the sender by return email and delete this email from your system. /font ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org yep man swapon though this won't be as elegant as having it set up as normal swap -- Dave Robison Sales Solution Architect II FIS Banking Solutions 510/621-2089 (w) 530/518-5194 (c) 510/621-2020 (f) da...@vicor.com david.robi...@fisglobal.com _ The information contained in this message is proprietary and/or confidential. If you are not the intended recipient, please: (i) delete the message and all copies; (ii) do not disclose, distribute or use the message in any manner; and (iii) notify the sender immediately. In addition, please be aware that any message addressed to our domain is subject to archiving and review by persons other than the intended recipient. Thank you. _ ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: swap pager:indefinite wait buffer: message out of vm.c
On 12/01/2010 03:23 PM, Mark Terribile wrote: Hi, Would some kind soul please tell me the meaning of a message coming from vm.c (FreeBSD 7.2): swap pager: indefinite wait buffer: bufobj: 0, blkno: 2, size: 4096 This message occurs after a return from an msleep whose last args are PSWP, swread, and HZ*20 . When it occurs, some interactive program is locked up. It recovers sometime later. My best guess is that this is a complaint that swap or paging I/O has been excessively delayed. It is occurring while I am running disk-to-disk transfers that have deep buffering. Think mbuf(1), but it's my own code, testing some algorithms. I speculate that if the disk queuing/head movement optimization doesn't let the heads move off the file system where the file resides (and I only see this with large, single files) then this problem might result. But that is a guess, and speculation. Does anyone know if this can occur under later versions of FreeBSD? Hi Mark, Do you have any test cases that reliably reproduce the problem? I've seen it crop up very infrequently on 8.1-RELEASE but I haven't been able to reproduce it. -- Benjamin Lee http://www.b1c1l1.com/ signature.asc Description: OpenPGP digital signature
Re: Swap on ZFS
On 7 October 2010 21:20, Anselm Strauss amsiba...@gmail.com wrote: On 10/02/10 17:52, Adam Vande More wrote: On Sat, Oct 2, 2010 at 4:30 AM, Anselm Strauss amsiba...@gmail.com wrote: Hi I have a virtual server with only 512 MB of memory but still want to run ZFS on it. snip Has there been any fix or workaround for this? I guess it does not help when I use a swap file on ZFS instead of a separate zvol. Make sure you are following this: http://wiki.freebsd.org/RootOnZFS/GPTZFSBoot Please note swap is not a ZVOL, it is a sepate partition. You'd have the same problem with ZVOL. Also use i386, that will save you a bit of memory. Follow the ZFS tuning guide. Even if you follow all those things, I'm not sure you'll be able to get it stable. 512MB is really tight. I now have the swap on a separate disk and it seems more stable. Although the server still has only 512 MB of RAM, runs on amd64 and I did no tuning. It's not a file server but compiling ports and running some services seems okay. I have seen multiple posts on the net where people put swap on ZFS. What sense does it make when every time the machine runs out of physical memory it freezes before it can allocate some swap memory. Does it only make sense in case you have additional non-ZFS swap? ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org there must be some logic in is as when you build a (open)*solaris box on zfs, the swap is on a vdev by defaukt. I think its because ZFS runs in kernel memory and this isn't swapable. Please correct me if im wrong somebody. $ swap -lh swapfile devswaplo blocks free /dev/zvol/dsk/rpool/swap 182,24K 2.0G 2.0G $ uname -a SunOS desktop2 5.11 snv_134 i86pc i386 i86pc Solaris ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Swap on ZFS
On 10/02/10 17:52, Adam Vande More wrote: On Sat, Oct 2, 2010 at 4:30 AM, Anselm Strauss amsiba...@gmail.com wrote: Hi I have a virtual server with only 512 MB of memory but still want to run ZFS on it. snip Has there been any fix or workaround for this? I guess it does not help when I use a swap file on ZFS instead of a separate zvol. Make sure you are following this: http://wiki.freebsd.org/RootOnZFS/GPTZFSBoot Please note swap is not a ZVOL, it is a sepate partition. You'd have the same problem with ZVOL. Also use i386, that will save you a bit of memory. Follow the ZFS tuning guide. Even if you follow all those things, I'm not sure you'll be able to get it stable. 512MB is really tight. I now have the swap on a separate disk and it seems more stable. Although the server still has only 512 MB of RAM, runs on amd64 and I did no tuning. It's not a file server but compiling ports and running some services seems okay. I have seen multiple posts on the net where people put swap on ZFS. What sense does it make when every time the machine runs out of physical memory it freezes before it can allocate some swap memory. Does it only make sense in case you have additional non-ZFS swap? ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Swap on ZFS
On Sat, Oct 2, 2010 at 4:30 AM, Anselm Strauss amsiba...@gmail.com wrote: Hi I have a virtual server with only 512 MB of memory but still want to run ZFS on it. snip Has there been any fix or workaround for this? I guess it does not help when I use a swap file on ZFS instead of a separate zvol. Make sure you are following this: http://wiki.freebsd.org/RootOnZFS/GPTZFSBoot Please note swap is not a ZVOL, it is a sepate partition. You'd have the same problem with ZVOL. Also use i386, that will save you a bit of memory. Follow the ZFS tuning guide. Even if you follow all those things, I'm not sure you'll be able to get it stable. 512MB is really tight. -- Adam Vande More ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Swap Partition First?
I figured out a way to install swap as the only fixed-sized partition such that whatever is left is marked as BSD (165) but I am not sure if this is a workable solution so I am asking for suggestions. If I set up the disk label reference file as follows: # /dev/ad0s1: 8 partitions: #size offsetfstype [fsize bsize bps/cpg] a: * 20971524.2BSD 2048 16384 28552 b: 20971520 swap bsdlabel gets very confused and one ends up with possibly swap and about 4 gigabytes of FreeBSD which is not right. So, I inverted things since what we want is for everything but swap to be FreeBSD and we want this to work on some disk for which we may not know the size. # /dev/ad0s1: 8 partitions: #size offsetfstype [fsize bsize bps/cpg] a: 20971520 swap b: * 20971524.2BSD 2048 16384 28552 This means one mounts ad0s1b instead of ad0s1a which is what you normally see. Will this create some sort of monster later down the line? The hope is to create a largely automated process that coworkers can use if we ever need to recreate X or Y server from a new piece of hardware during an upgrade or after a lightening storm when every minute counts. Many thanks. Martin McCormick WB5AGZ Stillwater, OK Systems Engineer OSU Information Technology Department Telecommunications Services Group ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Swap Partition First?
On Tue, Feb 02, 2010 at 11:28:13AM -0600, Martin McCormick wrote:
I figured out a way to install swap as the only
fixed-sized partition such that whatever is left is marked as
BSD (165) but I am not sure if this is a workable solution so I
am asking for suggestions.
If I set up the disk label reference file as follows:
# /dev/ad0s1:
8 partitions:
#size offsetfstype [fsize bsize bps/cpg]
a: * 20971524.2BSD 2048 16384 28552
b: 20971520 swap
bsdlabel gets very confused and one ends up with possibly swap
and about 4 gigabytes of FreeBSD which is not right.
This could be a problem. I think using the '*' for size will
cause it to use the whole remaining space for that partition.
Even though it logically starts at 2097152, it might not come out
even on a good boundary or something like that. It really seems to
like to have things entered sequentially.
So, I inverted things since what we want is for
everything but swap to be FreeBSD and we want this to work on
some disk for which we may not know the size.
# /dev/ad0s1:
8 partitions:
#size offsetfstype [fsize bsize bps/cpg]
a: 20971520 swap
b: * 20971524.2BSD 2048 16384 28552
This means one mounts ad0s1b instead of ad0s1a which is
what you normally see. Will this create some sort of monster
later down the line?
It should not create a problem in the system, but it might
introduce some confusion later when you have partly forgotten
what you did and why. So, you might want to keep the swap
on 'b' since it is a strong convention.
You could have left the 'a' partition empty; just not used it.
Then make 'b' your swap with the fixed size as usual and then
something like 'd' (or 'e' or 'f' or 'g' or 'h') be that large
partition using up all the rest of the space.
Although it seems to prefer the space be claimed in order, it
has no problem ignoring skipped partition letters.
If I use up a who extra disk in one slice-partition, I usually
make it 'd' or 'h' and skip 'a', 'b' (and of course, 'c') just to
keep things clear in my head.
Something like:
# /dev/ad0s1:
8 partitions:
#sizeoffsetfstype [fsize bsize bps/cpg]
b: 2097152 0 swap
g:* *4.2BSD 2048 16384 28552
Should work just fine.
The hope is to create a largely automated process that
coworkers can use if we ever need to recreate X or Y server from
a new piece of hardware during an upgrade or after a lightening
storm when every minute counts. Many thanks.
So, in that case, do stick closer to convention and use a higher
partition label identifier such as 'd' or whatever, as above.
In fact set yourself up with a conventional use for each identifier
so that it can be used in all circumstances. Such as:
a = root(if the disk doesn't have root skip 'a')
b = swap('' '' '' '' '' swap '' 'b')
c = reserved for system
d = /tmp( etc )
e = /usr( etc )
f = /var( etc )
g = /home ( etc )
h = /work extra big space to put stuff. ( etc )
Just use the ones needed and skip the others. But still enter
the ones you use in their conventional order in bsdlabel.
jerry
Martin McCormick WB5AGZ Stillwater, OK
Systems Engineer
OSU Information Technology Department Telecommunications Services Group
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Re: Swap Partition First?
Jerry McAllister writes: This could be a problem. I think using the '*' for size will cause it to use the whole remaining space for that partition. Even though it logically starts at 2097152, it might not come out even on a good boundary or something like that. It really seems to like to have things entered sequentially. It should not create a problem in the system, but it might introduce some confusion later when you have partly forgotten what you did and why. So, you might want to keep the swap on 'b' since it is a strong convention. Thanks for all the excellent suggestions, here. I may write a shell script that runs fdisk and captures the number of total blocks and subtracts from that value the size of swap. That would make it possible to generate a totally conventional bsdlabel file in the order we are used to having the partitions in. This would just be a part of the script that the person building the new system would run without having to know precisely how to format the drive. Our group has several members who would do just fine in setting up a system if guided over some of the rough parts by a good script. The challenge is to come up with something that does not give someone the rope to hang themselves accidentally. I am lucky in that I have a couple of old systems to do horrible things to that are too slow and old for anybody else to need. Again, thank you. Martin McCormick WB5AGZ Stillwater, OK Systems Engineer OSU Information Technology Department Telecommunications Services Group ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Swap Partition First? Something is still Wrong.
When referring to the slices in a FreeBSD partition, which is correct, ad0s1a or ad0s1-1? One of the problems in setting up install.cfg is that I am not sure if it is not configuring the disk because the designations are wrong or if I am telling fdisk to do something that it can't do. ad0s1-1=ufs 77116032 / 1 ad0s1-2=swap 0 or should it be ad0s1a and ad0s1b? When using ad0s1a and ad0s1b, there are no error messages, but it also didn't create the swap partition. Thank you. Martin McCormick ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Swap Partition First?
The only thing that looks out of place is that you have defined ad0s1-2 before ad0s1-1. I've never tested it, but perhaps this is causing it to get confused when calculating the disk layout? In other words, perhaps you should use #1G swap followed by / on rest of disk. # ad0s1-1=swap 2097152 #All the rest is FreeBSD with soft updates. ad0s1-2=ufs 0 / 1 so they are defined in numerical sequence. On 1/27/10, Martin McCormick mar...@dc.cis.okstate.edu wrote: Our FreeBSD systems mostly have a very simple disk layout. There is a 1 or 2-gigabyte swap partition and all the rest is FreeBSD. When manually configuring these partitions in sysinstall, I usually set up swap first with a 1GB size and then use the remaining space by selecting the values as defaults. An attempt to script this in an install.cfg file is not going well. The disk formatting part of the file is as follows: disk=ad0 partition=all bootManager=none diskPartitionEditor #Entire disk is FreeBSD. diskPartitionWrite # All sizes are expressed in 512 byte blocks! # #1G swap followed by / on rest of disk. # ad0s1-2=swap 2097152 #All the rest is FreeBSD with soft updates. ad0s1-1=ufs 0 / 1 # Let's do it! diskLabelEditor diskLabelCommit # OK, everything is set. Do it! installCommit This doesn't work. sysinstall reports that it can't write the swap space. fdisk reports a FreeBSD partition and all the others are shown as free. Any ideas? Thank you. Martin McCormick WB5AGZ Stillwater, OK Systems Engineer OSU Information Technology Department Telecommunications Services Group ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org -- -- Bob Johnson fbsdli...@gmail.com ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Swap Partition First?
Bob Johnson writes: The only thing that looks out of place is that you have defined ad0s1-2 before ad0s1-1. I've never tested it, but perhaps this is causing it to get confused when calculating the disk layout? In other words, perhaps you should use #1G swap followed by / on rest of disk. Thank you. I wondered about that. I didn't know how smart the allocater was. Technically, when I defined ad0s1-1 as being the rest of the disk, nothing else had been defined yet so that should mean 100% of the disk. That's called thinking too much. Martin McCormick ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Swap and memory optimization
I would just bump the ram to 2gigs or 4 if it supports it and call it good. You should be fine. On Thu, Oct 1, 2009 at 8:58 AM, Bill Moran wmo...@potentialtech.com wrote: In response to Dan Nelson dnel...@allantgroup.com: In the last episode (Oct 01), Bill Moran said: bsd b...@todoo.biz wrote: I have a FBSD 6.4p7 box that I use as a mail server - 1Go RAM - RAID1 Works quite well. As I plan to put 100 more mail accounts soon on the server I was wondering if the memory swap was ok on the server considering these figures: last pid: 18956; load averages: 0.04, 0.11, 0.05 up 19+08:36:23 09:53:38 125 processes: 1 running, 124 sleeping CPU: 0.0% user, 0.0% nice, 1.5% system, 0.4% interrupt, 98.1% idle Mem: 499M Active, 70M Inact, 362M Wired, 41M Cache, 111M Buf, 20M Free Swap: 2000M Total, 160M Used, 1840M Free, 8% Inuse Though It looks good to me - the server swaps a bit (between 8 to 14%) and there is not much memory left. Looks like the server would run more smoothly with a bit more RAM. At least an additional 256M, I would think, but considering the price of RAM, you might as well just up it to 2G. The amount of used swap is much less important than whether you are actively swapping (if there are In/Out values on the Swap line in top, or if vmstat 1 shows nonzero values in the pi/po columns). 160MB of used swap is fine if it's just unused daemons (getty, idle webserver, etc). More memory can never hurt, but it doesn't seem like it's urgently needed here. I don't know about that, Dan. Especially considering it's a mail server he's talking about, there's no RAM left for disk cache on that machine. We've seen performance gains on our mail server by putting obscene amounts of RAM into it. After a bit of use, FreeBSD ends up having 6.5G of inactive RAM, which I assume is cache of mailboxes. The result is that while watching gstat, the amount of disk reads is very low (since a lot of data is already in RAM) and the IO is available to do fast writes when new mail comes in. -- Bill Moran http://www.potentialtech.com http://people.collaborativefusion.com/~wmoran/ ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org -- Who knew ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Swap and memory optimization
bsd b...@todoo.biz wrote: Hello, I have a FBSD 6.4p7 box that I use as a mail server - 1Go RAM - RAID1 Works quite well. As I plan to put 100 more mail accounts soon on the server I was wondering if the memory swap was ok on the server considering these figures: last pid: 18956; load averages: 0.04, 0.11, 0.05 up 19+08:36:23 09:53:38 125 processes: 1 running, 124 sleeping CPU: 0.0% user, 0.0% nice, 1.5% system, 0.4% interrupt, 98.1% idle Mem: 499M Active, 70M Inact, 362M Wired, 41M Cache, 111M Buf, 20M Free Swap: 2000M Total, 160M Used, 1840M Free, 8% Inuse Though It looks good to me - the server swaps a bit (between 8 to 14%) and there is not much memory left. Looks like the server would run more smoothly with a bit more RAM. At least an additional 256M, I would think, but considering the price of RAM, you might as well just up it to 2G. -- Bill Moran http://www.potentialtech.com ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Swap and memory optimization
On Thu, Oct 01, 2009 at 09:58:36AM +0200, bsd wrote: Hello, I have a FBSD 6.4p7 box that I use as a mail server - 1Go RAM - RAID1 Works quite well. As I plan to put 100 more mail accounts soon on the server I was wondering if the memory swap was ok on the server considering these figures: last pid: 18956; load averages: 0.04, 0.11, 0.05 up 19+08:36:23 09:53:38 125 processes: 1 running, 124 sleeping CPU: 0.0% user, 0.0% nice, 1.5% system, 0.4% interrupt, 98.1% idle Mem: 499M Active, 70M Inact, 362M Wired, 41M Cache, 111M Buf, 20M Free Swap: 2000M Total, 160M Used, 1840M Free, 8% Inuse Though It looks good to me - the server swaps a bit (between 8 to 14%) and there is not much memory left. Let me know what you think about these figures. Unless something else is going on or you are running some commercial server that gets huge amounts of traffic, you should have no capacity problem with this setup. You might want to upgrade to a more recent FreeBSD. jerry Thanks. Gregober --- PGP ID -- 0x1BA3C2FD bsd @at@ todoo.biz P Please consider your environmental responsibility before printing this e-mail ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Swap and memory optimization
In the last episode (Oct 01), Bill Moran said: bsd b...@todoo.biz wrote: I have a FBSD 6.4p7 box that I use as a mail server - 1Go RAM - RAID1 Works quite well. As I plan to put 100 more mail accounts soon on the server I was wondering if the memory swap was ok on the server considering these figures: last pid: 18956; load averages: 0.04, 0.11, 0.05 up 19+08:36:23 09:53:38 125 processes: 1 running, 124 sleeping CPU: 0.0% user, 0.0% nice, 1.5% system, 0.4% interrupt, 98.1% idle Mem: 499M Active, 70M Inact, 362M Wired, 41M Cache, 111M Buf, 20M Free Swap: 2000M Total, 160M Used, 1840M Free, 8% Inuse Though It looks good to me - the server swaps a bit (between 8 to 14%) and there is not much memory left. Looks like the server would run more smoothly with a bit more RAM. At least an additional 256M, I would think, but considering the price of RAM, you might as well just up it to 2G. The amount of used swap is much less important than whether you are actively swapping (if there are In/Out values on the Swap line in top, or if vmstat 1 shows nonzero values in the pi/po columns). 160MB of used swap is fine if it's just unused daemons (getty, idle webserver, etc). More memory can never hurt, but it doesn't seem like it's urgently needed here. -- Dan Nelson dnel...@allantgroup.com ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Swap and memory optimization
In response to Dan Nelson dnel...@allantgroup.com: In the last episode (Oct 01), Bill Moran said: bsd b...@todoo.biz wrote: I have a FBSD 6.4p7 box that I use as a mail server - 1Go RAM - RAID1 Works quite well. As I plan to put 100 more mail accounts soon on the server I was wondering if the memory swap was ok on the server considering these figures: last pid: 18956; load averages: 0.04, 0.11, 0.05 up 19+08:36:23 09:53:38 125 processes: 1 running, 124 sleeping CPU: 0.0% user, 0.0% nice, 1.5% system, 0.4% interrupt, 98.1% idle Mem: 499M Active, 70M Inact, 362M Wired, 41M Cache, 111M Buf, 20M Free Swap: 2000M Total, 160M Used, 1840M Free, 8% Inuse Though It looks good to me - the server swaps a bit (between 8 to 14%) and there is not much memory left. Looks like the server would run more smoothly with a bit more RAM. At least an additional 256M, I would think, but considering the price of RAM, you might as well just up it to 2G. The amount of used swap is much less important than whether you are actively swapping (if there are In/Out values on the Swap line in top, or if vmstat 1 shows nonzero values in the pi/po columns). 160MB of used swap is fine if it's just unused daemons (getty, idle webserver, etc). More memory can never hurt, but it doesn't seem like it's urgently needed here. I don't know about that, Dan. Especially considering it's a mail server he's talking about, there's no RAM left for disk cache on that machine. We've seen performance gains on our mail server by putting obscene amounts of RAM into it. After a bit of use, FreeBSD ends up having 6.5G of inactive RAM, which I assume is cache of mailboxes. The result is that while watching gstat, the amount of disk reads is very low (since a lot of data is already in RAM) and the IO is available to do fast writes when new mail comes in. -- Bill Moran http://www.potentialtech.com http://people.collaborativefusion.com/~wmoran/ ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Swap on ZFS - still a bad idea?
Putting swap on ZFS is listed as broken on the wiki. Is that still true of the newly MFC'ed version? No idea. You may just make separate partition for swapping and it will work. Good if you have swap just for sure. If your system needs swapping under normal operation, using ZFS is really bad idea as it needs lots of memory - which you are already short of. With RAM costs of 20$/GB (DDR2) it's best to get as much memory as your software needs. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Swap on ZFS - still a bad idea?
On Wednesday 03 June 2009 01:36:37 pm Wojciech Puchar wrote: No idea. You may just make separate partition for swapping and it will work. Good if you have swap just for sure. Well, the problem is that I wanted to have a bare-metal ZFS system without any FreeBSD slices or partitions. If your system needs swapping under normal operation, using ZFS is really bad idea as it needs lots of memory - which you are already short of. It was more of the just in case, with plenty of RAM for normal operation. -- Kirk Strauser ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Swap on ZFS - still a bad idea?
On Wednesday 03 June 2009 01:36:37 pm Wojciech Puchar wrote: No idea. You may just make separate partition for swapping and it will work. Good if you have swap just for sure. Well, the problem is that I wanted to have a bare-metal ZFS system without any FreeBSD slices or partitions. slices are not needed with any fs. partitions - you need at least boot partition. If your system needs swapping under normal operation, using ZFS is really bad idea as it needs lots of memory - which you are already short of. It was more of the just in case, with plenty of RAM for normal operation. -- so just don't set up swap at all, or do under ZFS as it's just in case not normal operation ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to freebsd-questions-unsubscr...@freebsd.org
Re: Swap partition
Eugen Udma wrote: Hello, I have FreeBSD installed on my desktop, with 2 GB of RAM and 4 GB swap partition and this swap partition is very seldom touched by the system and then only 2-3% used. I want to install FreeBSD on a laptop with 4 GB of RAM and a hard disk of 100 GB. Should I waste 8 GB for a swap partition, as it is recommended in the handbook? Thanks for any advice, Eugen In short, no. And in fact in order to use those 4GB RAM you will need either FreeBSD/amd64 or a PAE kernel. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: Swap partition
On Wed, Jan 02, 2008 at 05:13:28PM -0800, Eugen Udma wrote: Hello, I have FreeBSD installed on my desktop, with 2 GB of RAM and 4 GB swap partition and this swap partition is very seldom touched by the system and then only 2-3% used. I want to install FreeBSD on a laptop with 4 GB of RAM and a hard disk of 100 GB. Should I waste 8 GB for a swap partition, as it is recommended in the handbook? It is not wasted as swap. The system uses swap space for both swap and paging. The traditional reason for making swap be 2X ram is that the system uses swap for taking a crash dump and that would be enough to handle all of ram for tracing. You can get by with less. If you are not using your laptop for development and if you are not using it as a server with the usual large proliferation of processes being forked off for everything, then having less swap may well be reasonable. But, note that you are talking only a small percentage of your Hd space, so it is hardly worth quibbling about. jerry Thanks for any advice, Eugen Looking for the perfect gift? Give the gift of Flickr! http://www.flickr.com/gift/ ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED] ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: Swap partition
Jerry McAllister writes: But, note that you are talking only a small percentage of your Hd space, so it is hardly worth quibbling about. In most places, disk space is dirt cheap. If you're really worried, find a 5-10 gbyte drive used and make it a dedicated swap disk. Robert Huff ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: Swap partition
On Wed, 2 Jan 2008 17:13:28 -0800 (PST) Eugen Udma [EMAIL PROTECTED] wrote: I want to install FreeBSD on a laptop with 4 GB of RAM and a hard disk of 100 GB. Should I waste 8 GB for a swap partition, as it is recommended in the handbook? Probably not. The twice the ram rule is for people who may need to debug kernel panics. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: Swap size
Jerry McAllister wrote: On Fri, Aug 17, 2007 at 02:05:57AM +0200, Nicholas Wieland wrote: I was reading tuning(7), and I found that I should size my swap double the size of my physical memory. AFAIK that was true some years ago, when memory was not as cheap as now, and following that guideline I should set my swap to 2GB, which seems far too much for swap (at least to me ...). I will never need this much memory as 1GB RAM and 2GB swap. Is it still correct ? How can I resize with bsdlabel if I already used all my disk space during install ? Remember, disk sizes have shot up too. No, 2 GB is not excessive. You can get by with less, but you're not likely to be using proportionately as much disk now as you used to by going with 2X - I aim for a little over 2X. Remember that swap gets used for crash dumps and also for paging. Now, you may think that you want to keep your machine from paging and in one sense that is true. If you are so memory bound that it has to page just to run, you're going to be so slow that it seems to have froze (by today's standards). But, the system does write stuff to page space and for processes that are often called it can speed things up. So, it is not really a waste to assign that much to swap. jerry TIA, ngw -- Nicholas Wieland [EMAIL PROTECTED] ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED] ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED] My understanding was that you should estimate swap size based on the sizes of the programs which might be paged out. However, when I first set up my system, I didn't know this and created 1G swap slices (one on each disk) but I am not convinced that this was the best thing to do, since my system almost never uses a noticible percentage of the swap space. right now, I've got [EMAIL PROTECTED] fusefs-sshfs]$ swapinfo Device 1K-blocks UsedAvail Capacity /dev/ad0s1b.eli 1048576 1148 1047428 0% /dev/ad1s1b.eli 1048576 1096 1047480 0% Total 2097152 2244 2094908 0% And the system is under normal load. This system has 1G of RAM. Is there any sense in having this much swap space when it's not being used? ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: Swap size
--On Friday, August 17, 2007 11:07:14 -0400 Andy Greenwood [EMAIL PROTECTED] wrote: Jerry McAllister wrote: On Fri, Aug 17, 2007 at 02:05:57AM +0200, Nicholas Wieland wrote: I was reading tuning(7), and I found that I should size my swap double the size of my physical memory. AFAIK that was true some years ago, when memory was not as cheap as now, and following that guideline I should set my swap to 2GB, which seems far too much for swap (at least to me ...). I will never need this much memory as 1GB RAM and 2GB swap. Is it still correct ? How can I resize with bsdlabel if I already used all my disk space during install ? Remember, disk sizes have shot up too. No, 2 GB is not excessive. You can get by with less, but you're not likely to be using proportionately as much disk now as you used to by going with 2X - I aim for a little over 2X. Remember that swap gets used for crash dumps and also for paging. Now, you may think that you want to keep your machine from paging and in one sense that is true. If you are so memory bound that it has to page just to run, you're going to be so slow that it seems to have froze (by today's standards). But, the system does write stuff to page space and for processes that are often called it can speed things up. So, it is not really a waste to assign that much to swap. jerry TIA, ngw -- Nicholas Wieland [EMAIL PROTECTED] ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED] ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED] My understanding was that you should estimate swap size based on the sizes of the programs which might be paged out. However, when I first set up my system, I didn't know this and created 1G swap slices (one on each disk) but I am not convinced that this was the best thing to do, since my system almost never uses a noticible percentage of the swap space. right now, I've got [EMAIL PROTECTED] fusefs-sshfs]$ swapinfo Device 1K-blocks UsedAvail Capacity /dev/ad0s1b.eli 1048576 1148 1047428 0% /dev/ad1s1b.eli 1048576 1096 1047480 0% Total 2097152 2244 2094908 0% And the system is under normal load. This system has 1G of RAM. Is there any sense in having this much swap space when it's not being used? Yes. As was stated earlier, you will need that much space to save a core file if the system crashes. If you don't care about troubleshooting major system crashes, then don't worry about it. OTOH, disk sizes have grown so large that 2GB of swap is negligible use of space. I always configure swap to be 2xRAM plus 200MB. On a 300GB drive, that's less than 1% of the space available. -- Paul Schmehl ([EMAIL PROTECTED]) Senior Information Security Analyst The University of Texas at Dallas http://www.utdallas.edu/ir/security/
Re: Swap size
On Fri, Aug 17, 2007 at 02:05:57AM +0200, Nicholas Wieland wrote: I was reading tuning(7), and I found that I should size my swap double the size of my physical memory. AFAIK that was true some years ago, when memory was not as cheap as now, and following that guideline I should set my swap to 2GB, which seems far too much for swap (at least to me ...). I will never need this much memory as 1GB RAM and 2GB swap. Is it still correct ? How can I resize with bsdlabel if I already used all my disk space during install ? Remember, disk sizes have shot up too. No, 2 GB is not excessive. You can get by with less, but you're not likely to be using proportionately as much disk now as you used to by going with 2X - I aim for a little over 2X. Remember that swap gets used for crash dumps and also for paging. Now, you may think that you want to keep your machine from paging and in one sense that is true. If you are so memory bound that it has to page just to run, you're going to be so slow that it seems to have froze (by today's standards). But, the system does write stuff to page space and for processes that are often called it can speed things up. So, it is not really a waste to assign that much to swap. jerry TIA, ngw -- Nicholas Wieland [EMAIL PROTECTED] ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED] ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: Swap size
Andy Greenwood writes: And the system is under normal load. This system has 1G of RAM. Is there any sense in having this much swap space when it's not being used? 1) It is - usually - better to have it and not need it, than need it and not have it. 2) While some machines have a very predictable working set of programs, others vary very widely. Trying to compute the right value is an exercise in futility. By default, I use the 2x current or expected memory rule split over as many physical disks as possible. Robert Huff ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: Swap size
On Fri, Aug 17, 2007 at 11:07:14AM -0400, Andy Greenwood wrote: My understanding was that you should estimate swap size based on the sizes of the programs which might be paged out. However, when I first set up my system, I didn't know this and created 1G swap slices (one on each disk) but I am not convinced that this was the best thing to do, since my system almost never uses a noticible percentage of the swap space. right now, I've got [EMAIL PROTECTED] fusefs-sshfs]$ swapinfo Device 1K-blocks UsedAvail Capacity /dev/ad0s1b.eli 1048576 1148 1047428 0% /dev/ad1s1b.eli 1048576 1096 1047480 0% Total 2097152 2244 2094908 0% And the system is under normal load. This system has 1G of RAM. Is there any sense in having this much swap space when it's not being used? swap is there to guard against overload conditions, not for normal load. If you are paging during normal operations your system performance will be terrible, so you want to make sure you have enough RAM that this does not happen. However, when a transient load spike comes in, would you prefer your system to slow down but keep working, or to kill off all your processes? Think of it as memory space insurance. Kris pgpvcvTfETSpH.pgp Description: PGP signature
Re: Swap size
On Fri, Aug 17, 2007 at 02:05:57AM +0200, Nicholas Wieland wrote: I was reading tuning(7), and I found that I should size my swap double the size of my physical memory. AFAIK that was true some years ago, when memory was not as cheap as now, and following that guideline I should set my swap to 2GB, which seems far too much for swap (at least to me ...). I will never need this much memory as 1GB RAM and 2GB swap. Is it still correct ? 2GB is a reasonable amount of swap space, and unless you plan to turn your system on and leave it in the closet doing nothing, it will use more memory than you think. How can I resize with bsdlabel if I already used all my disk space during install ? With a bit of work you can grow partitions (see growfs), but you cannot shrink them. Kris pgpxxpQnKJcpS.pgp Description: PGP signature
Re: Swap size
On Aug 16, 2007, at 7:05 PMAug 16, 2007, Nicholas Wieland wrote: I was reading tuning(7), and I found that I should size my swap double the size of my physical memory. AFAIK that was true some years ago, when memory was not as cheap as now, and following that guideline I should set my swap to 2GB, which seems far too much for swap (at least to me ...). I will never need this much memory as 1GB RAM and 2GB swap. Is it still correct ? How can I resize with bsdlabel if I already used all my disk space during install ? TIA, ngw From what I understand, the reasoning behind the math is that, if you have a kernel dump, there's enough room in swap to put the entire core into swap (so it's there when you've rebooted), and that there's enough room left in swap to allow the system to reboot, so you can debug. If you're not worried about your .core files, then I wouldn't worry about the math of 2xmemory. HTH - Eric F Crist Secure Computing Networks ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: Swap size
At 03:03 AM 7/19/2007, Gabriel Linder wrote: Hi, I plan to setup FreeBSD 6.2-RELEASE on my Core Duo laptop with 1GB of RAM. The handbook says ideal swap size is 2xRAM, so should I use 2GB of swap ? Yes unless you know how many applications will ever be run and their run size. The 2xRAM is so you can always have a reasonable performance allowing swap. You can still run out of swap, and this will cause a panic. With disks so cheap, why not use 2XRAM? This seems a bit huge to me, I never used more than 400MB on Linux. If so, is there a limit of swap partition size (or number) on i386 (for Linux it's 2GB per partition and 32 partitions max, but I don't know for FreeBSD) ? You can add more swap using a swap file you can check that out doing: man swapon I don't believe there is a limit to swap partitions, other than the limit on other partitions. I have no knowledge on efficiency of a swap partition vs a swap file. -Derek -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean. MailScanner thanks transtec Computers for their support. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: Swap size
Derek Ragona wrote: At 03:03 AM 7/19/2007, Gabriel Linder wrote: Hi, I plan to setup FreeBSD 6.2-RELEASE on my Core Duo laptop with 1GB of RAM. The handbook says ideal swap size is 2xRAM, so should I use 2GB of swap ? Yes unless you know how many applications will ever be run and their run size. The 2xRAM is so you can always have a reasonable performance allowing swap. You can still run out of swap, and this will cause a panic. With disks so cheap, why not use 2XRAM? Running out of swap doesn't cause a panic, it causes the largest process to be killed. This seems a bit huge to me, I never used more than 400MB on Linux. If so, is there a limit of swap partition size (or number) on i386 (for Linux it's 2GB per partition and 32 partitions max, but I don't know for FreeBSD) ? For a Desktop System 400M should be enough, I don't remember my Desktop system to ever use more than 1m of swap. However, the swap size should be large enough for a dump during a panic. So if you want to be able to do some debugging if you ever run into panics, your swap should be at least as large as your memory. Assuming that you might add more memory one day something between 2 or 4GB of swap look reasonable to me. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: Swap size
[LoN]Kamikaze wrote: Derek Ragona wrote: At 03:03 AM 7/19/2007, Gabriel Linder wrote: Hi, I plan to setup FreeBSD 6.2-RELEASE on my Core Duo laptop with 1GB of RAM. The handbook says ideal swap size is 2xRAM, so should I use 2GB of swap ? Yes unless you know how many applications will ever be run and their run size. The 2xRAM is so you can always have a reasonable performance allowing swap. You can still run out of swap, and this will cause a panic. With disks so cheap, why not use 2XRAM? Running out of swap doesn't cause a panic, it causes the largest process to be killed. This seems a bit huge to me, I never used more than 400MB on Linux. If so, is there a limit of swap partition size (or number) on i386 (for Linux it's 2GB per partition and 32 partitions max, but I don't know for FreeBSD) ? For a Desktop System 400M should be enough, I don't remember my Desktop system to ever use more than 1m of swap. However, the swap size should be large enough for a dump during a panic. So if you want to be able to do some debugging if you ever run into panics, your swap should be at least as large as your memory. Assuming that you might add more memory one day something between 2 or 4GB of swap look reasonable to me. Thanks for the precisions, I will go for 2xRAM so. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: swap file vs swap partition
On Sun, Feb 04, 2007 at 03:24:39PM -0800, Aloha Guy wrote: What I actually meant was, I know in the old days, if you had 128MB, you want a 256MB swap but with 2GB RAM, isn't 4GB going to be overkill for a swap or are you saying that a 2GB swap will work? I'm still lost on the ratio since I thought the 2x was only if you had like small amounts of RAM. It really depends on what you are doing with the system. The system also pages to swap space. Now, you really want enough ram so that you are not depending on paging while something is running, but if you have lots of processes with many kind of resting until something comes up, the system may gradually use up their in-core space for other stuff, even though the process is not actually swapped out. Then, if some of those processes have to run again, they don't half to be built up again. The system just pulls back in the pages it needs - not necessarily the whole thing. It is, then good to have enough space for that. It would take some observation on how your system is used to decide just how important your swap size is. If you are running a big enough system that 4 GB of ram is needed, then 4 GB or even 8 GB swap is not so comparatively large. You would probably be running disk sizes in 70-160 GB size and maybe more than one, so what's 4 GB! Anyway, you want to have enough swap to cover a crash-dump - not that it is a frequent occurance unless you are doing development. After all, this is FreeBSD, not MS. But, still, it is good to have. jerry ps. Please learn to break your text lines at about 70 characters. It makes responding much easier. /jrm John - Original Message From: Scott Long [EMAIL PROTECTED] To: Aloha Guy [EMAIL PROTECTED] Cc: [EMAIL PROTECTED]; [EMAIL PROTECTED] Sent: Sunday, February 4, 2007 2:28:47 PM Subject: Re: swap file vs swap partition Aloha Guy wrote: Thanks for the input. You do have good points. The only issue with swap partitions is that it seems like you need to increase it everytime you increase the physical memory. Is there a swap partition size limit that pretty much will handle anything and setting a number larger than that will really not offer anything? John Processors and memory have vastly outpaced the speed of disks; any amount of swapping is going to be percieved as being very slow and something that should be avoided. Since RAM is also very cheap now, most people just load enough RAM into their system to handle their load, and then configure enough swap to hold a crashdump of that RAM. You always want swap so that you can handle unexpected spikes in load without crashing, but it's less of an integral piece of normal system operation these days. Scott It's here! Your new message! Get new email alerts with the free Yahoo! Toolbar. http://tools.search.yahoo.com/toolbar/features/mail/ ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED] ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: swap file vs swap partition
Aloha Guy wrote: Greetings everyone: I am planning to build a few new boxes which will run -RELEASE and -CURRENT and I have a question about the swap file. In the past, I had always used a swap partition of 256MB since I originally had 128MB system memory in the 1990's but my system has been upgraded to 2GB and it seems the swap file would have more flexibility as I can just change the size of the swapfile if I needed to. My question is is there any difference in performance between a swap file versus a swap partition and can one run a system with a swap file instead of a swap partition? Yes. A swap file requires a pass through the filesystem code in order to figure out where each block is. Also, searching has not gotten me very far but are there any drawbacks to a swap file instead of a swap partition? I read somewhere that a few people seem to think that a swap file can't handle kernel crash dumps? That's correct, it cannot. Shouldn't it be the same as both of them occupy disk space and as long as the swap file is large enough, wouldn't it work? The crashdump code is written to assume that the dump space is completely contiguous, something that is not at all guaranteed by a swap file. While it would certainly be possible to modify it to make a pass through the filesystem like above, the intention of the crashdump code is also to be as simple as possible and to depend on as few kernel services as possible. When the system has crashed, who knows what can be trusted anymore, right? Also, filesystem corruption is a frequent cause of crashes; why risk that dumping to a swapfile might encounter corruption and trash your entire filesystem. Scott ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: swap file vs swap partition
Thanks for the input. You do have good points. The only issue with swap partitions is that it seems like you need to increase it everytime you increase the physical memory. Is there a swap partition size limit that pretty much will handle anything and setting a number larger than that will really not offer anything? John - Original Message From: Scott Long [EMAIL PROTECTED] To: Aloha Guy [EMAIL PROTECTED] Cc: [EMAIL PROTECTED]; [EMAIL PROTECTED] Sent: Sunday, February 4, 2007 12:16:37 PM Subject: Re: swap file vs swap partition Aloha Guy wrote: Greetings everyone: I am planning to build a few new boxes which will run -RELEASE and -CURRENT and I have a question about the swap file. In the past, I had always used a swap partition of 256MB since I originally had 128MB system memory in the 1990's but my system has been upgraded to 2GB and it seems the swap file would have more flexibility as I can just change the size of the swapfile if I needed to. My question is is there any difference in performance between a swap file versus a swap partition and can one run a system with a swap file instead of a swap partition? Yes. A swap file requires a pass through the filesystem code in order to figure out where each block is. Also, searching has not gotten me very far but are there any drawbacks to a swap file instead of a swap partition? I read somewhere that a few people seem to think that a swap file can't handle kernel crash dumps? That's correct, it cannot. Shouldn't it be the same as both of them occupy disk space and as long as the swap file is large enough, wouldn't it work? The crashdump code is written to assume that the dump space is completely contiguous, something that is not at all guaranteed by a swap file. While it would certainly be possible to modify it to make a pass through the filesystem like above, the intention of the crashdump code is also to be as simple as possible and to depend on as few kernel services as possible. When the system has crashed, who knows what can be trusted anymore, right? Also, filesystem corruption is a frequent cause of crashes; why risk that dumping to a swapfile might encounter corruption and trash your entire filesystem. Scott Get your own web address. Have a HUGE year through Yahoo! Small Business. http://smallbusiness.yahoo.com/domains/?p=BESTDEAL ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: swap file vs swap partition
Aloha Guy wrote: Thanks for the input. You do have good points. The only issue with swap partitions is that it seems like you need to increase it everytime you increase the physical memory. Is there a swap partition size limit that pretty much will handle anything and setting a number larger than that will really not offer anything? John Processors and memory have vastly outpaced the speed of disks; any amount of swapping is going to be percieved as being very slow and something that should be avoided. Since RAM is also very cheap now, most people just load enough RAM into their system to handle their load, and then configure enough swap to hold a crashdump of that RAM. You always want swap so that you can handle unexpected spikes in load without crashing, but it's less of an integral piece of normal system operation these days. Scott ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: swap file vs swap partition
What I actually meant was, I know in the old days, if you had 128MB, you want a 256MB swap but with 2GB RAM, isn't 4GB going to be overkill for a swap or are you saying that a 2GB swap will work? I'm still lost on the ratio since I thought the 2x was only if you had like small amounts of RAM. John - Original Message From: Scott Long [EMAIL PROTECTED] To: Aloha Guy [EMAIL PROTECTED] Cc: [EMAIL PROTECTED]; [EMAIL PROTECTED] Sent: Sunday, February 4, 2007 2:28:47 PM Subject: Re: swap file vs swap partition Aloha Guy wrote: Thanks for the input. You do have good points. The only issue with swap partitions is that it seems like you need to increase it everytime you increase the physical memory. Is there a swap partition size limit that pretty much will handle anything and setting a number larger than that will really not offer anything? John Processors and memory have vastly outpaced the speed of disks; any amount of swapping is going to be percieved as being very slow and something that should be avoided. Since RAM is also very cheap now, most people just load enough RAM into their system to handle their load, and then configure enough swap to hold a crashdump of that RAM. You always want swap so that you can handle unexpected spikes in load without crashing, but it's less of an integral piece of normal system operation these days. Scott It's here! Your new message! Get new email alerts with the free Yahoo! Toolbar. http://tools.search.yahoo.com/toolbar/features/mail/ ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: swap file vs swap partition
On Monday 05 February 2007 08:58, Scott Long wrote: Processors and memory have vastly outpaced the speed of disks; any amount of swapping is going to be percieved as being very slow and something that should be avoided. Since RAM is also very cheap now, most people just load enough RAM into their system to handle their load, and then configure enough swap to hold a crashdump of that RAM. You always want swap so that you can handle unexpected spikes in load without crashing, but it's less of an integral piece of normal system operation these days. Mini-dumps have made it a lot easier to get away with a small amount of swap. That said it's not like disk is expensive either! -- Daniel O'Connor software and network engineer for Genesis Software - http://www.gsoft.com.au The nice thing about standards is that there are so many of them to choose from. -- Andrew Tanenbaum GPG Fingerprint - 5596 B766 97C0 0E94 4347 295E E593 DC20 7B3F CE8C pgpzXapmx8DNB.pgp Description: PGP signature
Re: swap file vs swap partition
On Sun, February 4, 2007 3:53 pm, Aloha Guy wrote: Thanks for the input. You do have good points. The only issue with swap partitions is that it seems like you need to increase it everytime you increase the physical memory. Is there a swap partition size limit that pretty much will handle anything and setting a number larger than that will really not offer anything? What you *might* consider doing: A swap partition the size of *ONE* RAM chip. A swap file the size of all your RAM chips. If you are having kernel panics, you can pull out RAM and then get your kernel dump, I would presume. This is a made-up answer from a guy who has no idea what he's talking about, really... -- Some people have a gift link here. Know what I want? I want you to buy a CD from some starving artist. http://cdbaby.com/browse/from/lynch Yeah, I get a buck. So? ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: swap file vs swap partition
Please wrap your lines and don't top-post. On Sun, 2007-Feb-04 15:24:39 -0800, Aloha Guy wrote: What I actually meant was, I know in the old days, if you had 128MB, you want a 256MB swap but with 2GB RAM, isn't 4GB going to be overkill for a swap or are you saying that a 2GB swap will work? I'm still lost on the ratio since I thought the 2x was only if you had like small amounts of RAM. 2:1 was a very old rule of thumb. A better approach is to consider your workload: Your working set needs to fit in RAM and the total virtual size needs to fit into RAM+swap. If you tend to leave lots of large processes lying around not doing anything, you might be able to usefully use much more swap than if you religiously kill processes that you aren't using - particularly if you don't have massive amounts of RAM. My desktop at work typically runs with swap utilisation about twice RAM (but it only has ~160MB RAM). Keep in mind that you can use multiple swap partitions so it can be useful to have an active swap on each disk. (The VM system stripes across available swaps). -- Peter Jeremy pgpMv9rkbZ7oC.pgp Description: PGP signature
Re: SWAP priority
Bob wrote: It became obvious after a short while, that I had too little physical memory (1GB), and I was using swap often. While swapping, things slowed down. So, I added an additional 1GB of swap space (via swap file) on the secondary file system. I did this as per the manual. I now have more swap; my question is this: How can I tell the OS to use the new swap file BEFORE using the old one? Is there a way to tell the system to prioritize the use of multiple swaps? The swap system knows how to interleave data between the additional swap areas relatively efficiently, but if your current workload is so demanding that you need to use more than 2GB of swapspace on a machine with 1GB of RAM, you should add more RAM, not more swapspace -- -Chuck ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: SWAP priority
On Monday 02 October 2006 09:14, Chuck Swiger wrote: The swap system knows how to interleave data between the additional swap areas relatively efficiently, Yes I discovered that. The additional swap space was instantly used as soon as I activated it; and the added swap improved things measurably. Does the swap system take into account current disk activity when it decides to use a particular swap? that you need to use more than 2GB of swapspace on a machine with 1GB of RAM, you should add more RAM, not more swapspace It is on order. The basis for my question about swap priority was based on an observation that the slowdown was due to swapping AND heavy disk usage. I noticed that when snapshots were being made on the main drive (the one I am using all the time), all other processes went to slow-mode. You see, the lack of enough memory caused the system to swap, and it swapped to the heaviest used raid array. I thought if I could force the system to swap to the other raid array (much less used) with the new swapfile, things would improve even more. All will be cured when more ram is installed, but I thought it would be interesting playing with swap priority. Bob ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: SWAP priority
On Oct 2, 2006, at 2:06 PM, Bob wrote: On Monday 02 October 2006 09:14, Chuck Swiger wrote: The swap system knows how to interleave data between the additional swap areas relatively efficiently, Yes I discovered that. The additional swap space was instantly used as soon as I activated it; and the added swap improved things measurably. Does the swap system take into account current disk activity when it decides to use a particular swap? Sort of. The syncer process runs at idle priority, so normal I/O initiated by your processes will take priority over paging/swapping idle pages of RAM out. There may be additional logic involved to help balance I/O in terms of which swapfile is being used if one drive remains busier than another, but I am not completely familiar with FreeBSD's implementation. that you need to use more than 2GB of swapspace on a machine with 1GB of RAM, you should add more RAM, not more swapspace It is on order. The basis for my question about swap priority was based on an observation that the slowdown was due to swapping AND heavy disk usage. I noticed that when snapshots were being made on the main drive (the one I am using all the time), all other processes went to slow-mode. You see, the lack of enough memory caused the system to swap, and it swapped to the heaviest used raid array. I thought if I could force the system to swap to the other raid array (much less used) with the new swapfile, things would improve even more. Well, you might try benchmarking the system with both arrays used for swapping and with only the less-busy RAID array being used for swapping, and see which one does better. -- -Chuck ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: SWAP priority
On Monday 02 October 2006 14:23, Charles Swiger wrote: Well, you might try benchmarking the system with both arrays used for swapping and with only the less-busy RAID array being used for swapping, and see which one does better. Yes, this is what I will do; if not benchmark, at least get a subjective feel for which is faster. Sorry to be a pest, but how can I do what you suggest? My SWAP0 is a _partition_ on the raid0 volume , and SWAP1 is a swapfile on raid1 created as a Vnode; and activated in rc.conf by swapfile=/raid1/swap1 How can I tell FreeBSD to ignore the primary swap partition? I set that partition up during the online install process if I recall, and none of my /etc/ files seem to reference it directly :-( I will also want to double the size of SWAP1 to 2GB, so the experiment is comparing the same swap space; but that part is simplistic. Bob ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: SWAP priority
On Mon, 2 Oct 2006 16:31:47 -0400
Bob [EMAIL PROTECTED] wrote:
Sorry to be a pest, but how can I do what you suggest? My SWAP0 is a
_partition_ on the raid0 volume , and SWAP1 is a swapfile on raid1 created
as a Vnode; and activated in rc.conf by swapfile=/raid1/swap1
How can I tell FreeBSD to ignore the primary swap partition? I set that
partition up during the online install process if I recall, and none of
my /etc/ files seem to reference it directly :-(
comment out the line swapfile in rc.conf .
B
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Re: Swap Size Importance?
On Friday 29 September 2006 11:52, Chris wrote: As a standard practice, I've always configured swap file to be double the size of real ram split across system and data disk. For example, 8gb on da0 and 8gb on da1 if the system has 8g real ram. In practice, In 7 or 8 years, I've never seen swap used for anything but a few k of inactive processes and I would imagine if real active process swapping occurred, it would be an immediate indicator that the system that isn't responsive enough for use anymore and requires upgrade or tuning. Can't run a website process off disk and keep anyone coming to the site ;-). (BTW, I'm talking only about high end servers, not test boxes where I've seen lots of swapping). I'm at the point of attempting my first gvinum software raid-5 and realized, I need the entire disk storage of all three non-system drives to avoid pulling an 8gb chunk out of the drive sizes. The configuration is one scsi 72g system disk and 3 that will be used for the raid volume. I should mention I turn off dumps, haven't found the use for that in a production server since it should not be rebooting or it's back in the shop and another box is taking it's place. Is there any shortfall in performance or reliability to running production with swap equal in size to the 8gb of system memory? I can't think of any but don't want to make a hard to correct mistake once this thing goes in. Nope. I routinely run boxes with 512MB or 1GB of swap, even if the RAM size is much higher than that. You won't have anywhere to save a crashdump in that case, but you seem to already be aware of that. JN ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: Swap Size Importance?
On Fri, Sep 29, 2006 at 08:52:58AM -0700, Chris wrote: As a standard practice, I've always configured swap file to be double the size of real ram split across system and data disk. For example, 8gb on da0 and 8gb on da1 if the system has 8g real ram. In practice, In 7 or 8 years, I've never seen swap used for anything but a few k of inactive processes and I would imagine if real active process swapping occurred, it would be an immediate indicator that the system that isn't responsive enough for use anymore and requires upgrade or tuning. Can't run a website process off disk and keep anyone coming to the site ;-). (BTW, I'm talking only about high end servers, not test boxes where I've seen lots of swapping). I'm at the point of attempting my first gvinum software raid-5 and realized, I need the entire disk storage of all three non-system drives to avoid pulling an 8gb chunk out of the drive sizes. The configuration is one scsi 72g system disk and 3 that will be used for the raid volume. I should mention I turn off dumps, haven't found the use for that in a production server since it should not be rebooting or it's back in the shop and another box is taking it's place. Is there any shortfall in performance or reliability to running production with swap equal in size to the 8gb of system memory? I can't think of any but don't want to make a hard to correct mistake once this thing goes in. It really depends on the number and size of processes you will be running. It you have a large memory and generally run a mix of processes that will totally fit in memory, then it probably doesn't doesn't matter much. But, if you run enough to actually cause paging - which goes to swap space - then it becomes an issue. Also, I think some things that get pulled to execute often can get left in swap space and accessed more quickly that all the way from main disk each time. eg the system keeps track of what it has in swap and it is more efficient to read from swap - less overhead. But someone else should know more about that than I. jerry ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED] ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: Swap Size Importance?
On Sep 29, 2006, at 9:06 AM, Jerry McAllister wrote: On Fri, Sep 29, 2006 at 08:52:58AM -0700, Chris wrote: Is there any shortfall in performance or reliability to running production with swap equal in size to the 8gb of system memory? I doesn't matter much. But, if you run enough to actually cause paging - which goes to swap space - then it becomes an issue. Also, I am assuming that real paging of active processes is death to that server anyway and means something else has to be throttled back with tuning of network bufs, apache or mysql. Same for crash dumps, can't run a server that is taking dumps or you lose your traffic. I think some things that get pulled to execute often can get left in swap space and accessed more quickly that all the way from main disk each time. eg the system keeps track of what it has in swap and it is more efficient to read from swap - less overhead. But someone This is the part that concerned me. If one views a top on well running system and sees no swapping, I wanted to make certain there is no magic going on behind the scenes where processes have been mapped to swap in such a way that I could be currently benefitting from swap being higher than actual and not know it. If top is an accurate read on whether the system has placed high use processes in swap then it would suggest the first post is correct, and a memory rich system, where you configure to never exceed real memory, wastes that storage taken in swap. For expensive drives, given the sizes we use in RAM now, it's hard to justify. In the case of attempting this raid-5 configuration, it equates to the loss of 24G in scsi storage. I will run with 8g on the system drive. Thank you very much for the responses. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: swap
In the last episode (Sep 24), Pietro Cerutti said: 512 MB of Ram, 1024 MB of swap, 6.1-STABLE After some time my system begins swapping, which is normal. The weird thing is that swapping goes on even after closing the memory consuming programs. here's the output of top(1): Mem: 103M Active, 37M Inact, 107M Wired, 6656K Cache, 60M Buf, 240M Free Swap: 1024M Total, 106M Used, 918M Free, 10% Inuse I se no swapping here (that would show up as ###K In, ###K Out on the swap line). You have swap space in use but not actively used. Why the swapped pages don't get recalled back to main mamory (which has sufficient free space for them), freeing the swap device and thus speeding the system up? Once the kernel decides to swap a page, that area of swap is reserved until the process exits, even if the kernel pulls the data back from swap. That way if memory gets low again, the kernel knows it can quickly discard the in-RAM copy of the data (since there's already a copy in swap). Processes likely to have pages swapped out are gettylogin proceses for unused ttys, lpd, sshd and other long-running daemons, etc. There's no reason to pull those pages back into RAM because you're more likely to need that RAM for something else. -- Dan Nelson [EMAIL PROTECTED] ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: swap
On 9/24/06, Dan Nelson [EMAIL PROTECTED] wrote: Once the kernel decides to swap a page, that area of swap is reserved until the process exits, even if the kernel pulls the data back from swap. That way if memory gets low again, the kernel knows it can quickly discard the in-RAM copy of the data (since there's already a copy in swap). Thanx for the insight... -- Dan Nelson [EMAIL PROTECTED] -- Pietro Cerutti ICQ: 117293691 PGP: 0x9571F78E - ASCII Ribbon Campaign - against HTML e-mail and proprietary attachments www.asciiribbon.org ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: Swap Performance in 6.1?
On Wed, May 10, 2006 at 04:36:15PM -0700, Timothy Beyer wrote: I am curious if this problem has been resolved in 6.1: (it was previously on the FreeBSD 6.1 Open Issues page, but I don't see it there any more) http://www.tr.freebsd.org/releases/6.1R/todo.html swapping on 6.0 is slower than on 4.x Not done Performance on swap handling is much slower than 4.x and this can make a system essentially unusable when moderate paging activity is going on Has this been resolved, (I did not see anything about it in the 6.1 release notes, or the errata) or has it been deferred to a future release? (The reason why I ask this is that programs like Firefox and Xemacs use up all of my 1 GB of memory and I have noticed problems of this nature in 6.0) The TODO item should have been worded better. There is anecdotal evidence that it is slower, but no-one has actually measured it definitively. Therefore it will be deferred until the future, after someone has actual numbers showing whether/how much slower it is, or not. Kris pgpFcIrV4mnuZ.pgp Description: PGP signature
Re: swap - 2 HDs
On Fri, Dec 16, 2005 at 09:33:57AM -0300, Aguiar Magalhaes wrote:
I have a machine with: dual processor AMD 64 bits, 4
GB RAM and 2 HDs SCSI 73 GB.
How can I configure the swap area ?
If you haven't completed the install, make the swap during the
install when you configure the disks. If you've already finished the
install, the Handbook has a section[0] describing methods for adding
swap.
Is It recommended to configure swap area in both HDs ??
I don't see the point -- swap is where pages that don't fit in your
real memory go. It's less optimal than real memory in terms of
latency, but I don't see how two disks would make swap performance
much better.
How large ??
I'd suggest 1-4G of swap depending on whether you need to read full
dumps of the kernel/memory for debugging. If you don't, you'll
probably be fine with a lesser amount of swap, unless you'll be
running applications which will overload the memory.
[0]
http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/adding-swap-space.html
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