Re: Questions about software RAID
Guy wrote: Well, I agree with KISS, but from the operator's point of view! I want... snip Fair enough. But I think the point is - should you expect the mdadm command to do all that? or do you think that it would make sense to stick with a layered approach that allows anything from my Zaurus PDA to an S390 mainframe to use basic md - with the S390 probably layering some management sw like EVMS over the top of md/mdadm. The *nix command line tool philosophy has generally been do one thing and do it well. It does provide some confusion for newbies when they see a collection of tools - but try running the one-liner - or numerous others like it - on OSes or tools that take the monolithic approach. Also - should the LED control code be built into mdadm? And should Neil write it? Is that for Dell controllers? or IBM ones? or SGI ones? what about my homemade parallel port one? What about controlling the LEDs on my PDA? Or should it be a seperate bit of code that needs a wrapper script and plugs in to a modular system like - you guessed it - EVMS. And Guy, I know what *you* think :) And I think the EVMS folk would accept patches for your suggestions - including any LED control ones. I do think you would need to ask Neil to support mdadm --sync-/dev/sdc-to-replace-/dev/sdg-even-though-/dev/sdg-is-fine mdadm --use-/dev/sdc-and-make-/dev/sdg-spare which would be especially useful if /dev/sdg were part of a shared spares pool. David - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Questions about software RAID
David Greaves wrote: Guy wrote: Well, I agree with KISS, but from the operator's point of view! I want... [snip] Fair enough. [snip] should the LED control code be built into mdadm? Obviously not. But currently, a LED control app would have to pull information from /proc/mdstat, right? mdstat is a crappy place to derive any state from. It currently seems to have a dual purpose: - being a simple textual representation of RAID state for the user. - providing MD state information for userspace apps. That's not good. There seems to be an obvious lack of a properly thought out interface to notify userspace applications of MD events (disk failed -- go light a LED, etc). Please correct me if I'm on the wrong track, in which case the rest of this posting will be bogus. Maybe there are IOCTLs or such that I'm not aware of. I'm not sure how a proper interface could be done (so I'm basically just blabbering). ACPI has some sort of event system, but the MD one would need to be more flexible. For instance userspace apps has to pick up on MD events such as disk failures, even if the userspace app happens to not be running in the exact moment that the event occurs (due to system restart, daemon restart or what not). So the system that ACPI uses is probably unsuited. Perhaps a simple logfile would do. It's focus should be machine-readability (vs. human readability for mdstat). A userspace app could follow MD's state from the beginning (bootup, no devices discovered, logfile cleared), through device discovery and RAID assembly and to failing devices. By adding up the information in all the log lines, a userspace app could derive the current state of MD (which disks are dead..). Just a thought. - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Questions about software RAID
On Wed, Apr 20, 2005 at 11:26:28AM +0200, Molle Bestefich wrote: David Greaves wrote: Guy wrote: Well, I agree with KISS, but from the operator's point of view! I want... [snip] Fair enough. [snip] should the LED control code be built into mdadm? Obviously not. But currently, a LED control app would have to pull information from /proc/mdstat, right? mdstat is a crappy place to derive any state from. It currently seems to have a dual purpose: - being a simple textual representation of RAID state for the user. - providing MD state information for userspace apps. That's not good. I could not agree more. There seems to be an obvious lack of a properly thought out interface to notify userspace applications of MD events (disk failed -- go light a LED, etc). Please correct me if I'm on the wrong track, in which case the rest of this posting will be bogus. Maybe there are IOCTLs or such that I'm not aware of. I'm not sure how a proper interface could be done (so I'm basically just blabbering). ACPI has some sort of event system, but the MD one would need to be more flexible. For instance userspace apps has to pick up on MD events such as disk failures, even if the userspace app happens to not be running in the exact moment that the event occurs (due to system restart, daemon restart or what not). So the system that ACPI uses is probably unsuited. Perhaps a simple logfile would do. No, as it requires active polling. I think something like a netlink device would be more accurate, but I'm not a kernel guru. Herve -- _ (°= Hervé Eychenne //) Homepage: http://www.eychenne.org/ v_/_ WallFire project: http://www.wallfire.org/ - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Questions about software RAID
Molle Bestefich [EMAIL PROTECTED] wrote: There seems to be an obvious lack of a properly thought out interface to notify userspace applications of MD events (disk failed -- go light a LED, etc). Well, that's probably truish. I've been meaning to ask for a per-device sysctl interface for some time. Peter - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Questions about software RAID
On 2005-04-20T13:16:24, Peter T. Breuer [EMAIL PROTECTED] wrote: There seems to be an obvious lack of a properly thought out interface to notify userspace applications of MD events (disk failed -- go light a LED, etc). Well, that's probably truish. I've been meaning to ask for a per-device sysctl interface for some time. sysctl? Surely you mean sysfs... ;-) Sincerely, Lars Marowsky-Brée [EMAIL PROTECTED] -- High Availability Clustering SUSE Labs, Research and Development SUSE LINUX Products GmbH - A Novell Business - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Questions about software RAID
Guy == Guy [EMAIL PROTECTED] writes: Guy I want the failed disk to light a red LED. Guy I want the tray the disk is in to light a red LED. Guy I want the cabinet the tray is in to light a red LED. That's easy when you have a custom hardware RAID enclosure that you have control over. As you suggest yourself, it's not easy when you have off the shelf components. What happens in real storage systems is that the SCSI bus is monitored by a SAF-TE or SES chip. The OS (in this case the RAID controller firmware) will talk to the SAF-TE device or access the SES page to get information about hot swap events, failed disks, stopped fans, busted power supply, etc. I messed with a daemon to monitor enclosures implementing either of these two standards during the infancy of hotplug. I should probably look into that again. But obviously this would only apply to disk trays with suitable monitoring hardware. Guy I want the re-build to the new disk to start. Are you sure? How do you know that the disk you just inserted is something you want to use for the RAID? What if you hook up - say - a USB storage device to back up data before you start messing with things? You most definitely don't want the RAID to start scribbling over any random device you hook up to a system with a failed RAID device. In the HW RAID enclosure case that's easy - again because the whole tray is under the array firmware's control. Definining a generic resync-on-hotplug policy is not trivial. One policy that might work for most people is sync if a new disk is inserted on the same address (SCSI controller, channel, id, lun). But there's no one size fits all policy. And this is not just because Linux sucks. It's simply that a lot of the easy HW RAID features are a result of appropriately designed hardware. We can certainly make Linux work more smoothly on hardware that allows for monitoring and predictable addressing, etc. But in the low end it'll have to be a policy defined by the sysadmin. And we probably want to leave it a sysadmin configurable policy even if the hardware implements the required magic. -- Martin K. Petersen Wild Open Source, Inc. [EMAIL PROTECTED] http://www.wildopensource.com/ - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Questions about software RAID
Hervé Eychenne wrote: Molle Bestefich wrote: There seems to be an obvious lack of a properly thought out interface to notify userspace applications of MD events (disk failed -- go light a LED, etc). I'm not sure how a proper interface could be done (so I'm basically just blabbering). ACPI has some sort of event system, but the MD one would need to be more flexible. For instance userspace apps has to pick up on MD events such as disk failures, even if the userspace app happens to not be running in the exact moment that the event occurs (due to system restart, daemon restart or what not). So the system that ACPI uses is probably unsuited. Perhaps a simple logfile would do. It's focus should be machine-readability (vs. human readability for mdstat). A userspace app could follow MD's state from the beginning (bootup, no devices discovered, logfile cleared), through device discovery and RAID assembly and to failing devices. By adding up the information in all the log lines, a userspace app could derive the current state of MD (which disks are dead..). No, as it requires active polling. No it doesn't. Just tail -f the logfile (or /proc/ or /sys/ file), and your app will receive due notice exactly when something happens. Or use inotify. I think something like a netlink device would be more accurate, but I'm not a kernel guru. No idea how that works :-). If by accurate you mean you'll get a faster reaction, that's wrong as per above explanation. And I'll try to explain why a logfile in other respects are actually _more_ accurate. I can see why a logfile _seems_ wrong at first sight. But the idea that it allows you to (*also*!) see historic MD events instead of just the current status this instant seems compelling. - You can be sure that you haven't missed or lost any MD events. If your monitoring app crashes or restarts, just look in the log. (If you're unsure whether you've notified the admin on some event or not; I'm sure MD could log the disk's event counters. The monitoring app could keep it's own how far have I gotten event counter [on disk], so the app knows it's own status.) - If the log resides in eg. /proc/whatever, you can pipe it to an actual file. It could be pretty useful for debugging MD (attach your MD log, send a mail asking what happened, and it'll be clear to the super-md-dude at first sight). - Seems more convincing to enterprise customers that you can actually see MD's every move in the log. Makes it seem much more robust and reliable. - Really useful for debugging the monitoring app - Probably other advantages. Haven't really thought it trough that well :-). The problem, as I see it, is if it's worth the implementation trouble (is it any harder than to implement a netlink / what not interface? No idea!) - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
RE: Questions about software RAID
From: Martin K. Petersen [mailto:[EMAIL PROTECTED] Sent: Wednesday, April 20, 2005 11:49 AM To: Guy Cc: 'Frank Wittig'; [EMAIL PROTECTED]; linux-raid@vger.kernel.org Subject: Re: Questions about software RAID Guy == Guy [EMAIL PROTECTED] writes: Guy I want the failed disk to light a red LED. Guy I want the tray the disk is in to light a red LED. Guy I want the cabinet the tray is in to light a red LED. That's easy when you have a custom hardware RAID enclosure that you have control over. As you suggest yourself, it's not easy when you have off the shelf components. What happens in real storage systems is that the SCSI bus is monitored by a SAF-TE or SES chip. The OS (in this case the RAID controller firmware) will talk to the SAF-TE device or access the SES page to get information about hot swap events, failed disks, stopped fans, busted power supply, etc. I messed with a daemon to monitor enclosures implementing either of these two standards during the infancy of hotplug. I should probably look into that again. But obviously this would only apply to disk trays with suitable monitoring hardware. Guy I want the re-build to the new disk to start. Are you sure? How do you know that the disk you just inserted is something you want to use for the RAID? What if you hook up - say - a USB storage device to back up data before you start messing with things? You most definitely don't want the RAID to start scribbling over any random device you hook up to a system with a failed RAID device. Yes I am sure, but the new disk would be replacing the old disk. Same bus same slot same ID/LUN or whatever. This may not be reasonable with all bus types, but with SCSI/SCA it is. Also, my wish list would need to be defined when the system is setup, I would not expect all systems to work this way. It would be fine to have a user interface that indicated a new disk was found and prompt the user for permission to use it. My wish list would have prerequisites! Maybe EVMS, or some other special layer that can notice a disk has been removed and notice when a different disk has been installed. Only 1 partition, or full disk. You can't (should not) pull a disk that has 2 or more partitions just because 1 may be bad! Maybe more prerequisites that I can't determine. But, assuming I meet the theoretical prerequisites, I should be able to build a system that can be maintained by normal sysadmins. These admins may be called operators in some environments. But with today's tools you need a Linux expert to replace a disk. IMO. And I don't think that is acceptable! Don't get me wrong!!! I love Linux, but I want improvements and features! Guy In the HW RAID enclosure case that's easy - again because the whole tray is under the array firmware's control. Definining a generic resync-on-hotplug policy is not trivial. One policy that might work for most people is sync if a new disk is inserted on the same address (SCSI controller, channel, id, lun). But there's no one size fits all policy. And this is not just because Linux sucks. It's simply that a lot of the easy HW RAID features are a result of appropriately designed hardware. We can certainly make Linux work more smoothly on hardware that allows for monitoring and predictable addressing, etc. But in the low end it'll have to be a policy defined by the sysadmin. And we probably want to leave it a sysadmin configurable policy even if the hardware implements the required magic. -- Martin K. PetersenWild Open Source, Inc. [EMAIL PROTECTED] http://www.wildopensource.com/ - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Questions about software RAID
tmp [EMAIL PROTECTED] wrote: I've read man mdadm and man mdadm.conf but I certainly doesn't have an overview of software RAID. Then try using it instead/as well as reading about it, and you will obtain a more cmprehensive understanding. OK. The HOWTO describes mostly a raidtools context, however. Is the following correct then? mdadm.conf may be considered as the replacement for raidtab. When mdadm No. Mdadm (generally speaking) does NOT use a configuration file and that is perhaps its major difference wrt to raidtools. Tt's command line. You can see for yourself what the man page itself summarises as the differences (the one about not using a configuration file is #2 of 3): mdadm is a program that can be used to create, manage, and monitor MD devices. As such it provides a similar set of functionality to the raidtools packages. The key differ ences between mdadm and raidtools are: mdadm is a single program and not a collection of pro grams. mdadm can perform (almost) all of its functions with out having a configuration file and does not use one by default. Also mdadm helps with management of the configuration file. mdadm can provide information about your arrays (through Query, Detail, and Examine) that raidtools cannot. starts it consults this file and starts the raid arrays correspondingly. No. As far as I am aware, the config file contains such details of existing raid arrays as may conveniently be discovered during a physical scan, and as such cntains only redundant information that at most may save the cost of a physical scan during such operations as may require it. Feel free to correct me! This leads to the following: Then I'll ignore it :-). Is it correct that I can use whole disks (/dev/hdb) only if I make a partitionable array and thus creates the partitions UPON the raid mechanism? Incomprehensible, I am afraid. You can use either partitions or whole disks in a raid array. As far as I can see, partitionable arrays makes disk replacements easier Oh - you mean that the partitions can be recognized at bootup by the kernel. You say I can't boot from such a partitionable raid array. Is that correctly understood? Partitionable? Or partitioned? I'm not sure what you mean. You would be able to boot via lilo from a partitioned RAID1 array, since all lilo requires is a block map of here to read the kernel image from, and either component of the RAID1 would do, and I'm sure that lilo has been altered to allow the use of both/either components blockmap during its startup routines. I don't know if grub can boot from a RAID1 array but it strikes me as likely since it would be able to ignore the raid1-ness and boot successfully just as though it were a (pre-raid-aware) lilo. Can I grow a partitionable raid array if I replace the existing disks with larger ones later? Partitionable? Or partitioned? If you grew the array you would be extending it beyond the last partition. The partition table itself is n sector zero, so it is not affected. You would presumably next change the partitions to take advatage of the increased size available. Would you prefer manual partitioned disks, even though disk replacements are a bit more difficult? I don't understand. I guess that mdadm automatically writes persistent superblocks to all disks? By default, yes? I meant, the /dev/mdX has to be formatted, not the individual partitions. Still right? I'm not sure what you mean. You mean /dev/mdXy by individual partitions? So I could actually just pull out the disk, insert a new one and do a mdadm -a /dev/mdX /dev/sdY? You might want to check that the old has been removed as well as faulted first. I would imagine it is only faulted. But it doesn't matter. The RAID system won't detect the newly inserted disk itself? It obeys commands. You can program the hotplug system to add it in autmatically. Are there some HOWTO out there, that is up-to-date and is based on RAID usage with mdadm and kernel 2.6 instead of raidtools and kernel 2.2/2.4? What there is seems fine to me if you can use the mdadm equivalents instead of raidhotadd and raidsetfaulty and raidhotremve and mkraid. The config file is not needed. Peter - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Questions about software RAID
Luca Berra wrote: many people find it easier to understand if raid partitions are set to 0XFD. kernel autodetection is broken and should not be relied upon. Could you clarify what is broken? I understood that it was simplistic (ie if you have a raid0 built over a raid5 or something exotic then it may have problems) but essentially worked. Could it be : * broken for complex raid on raid * broken for root devices * fine for 'simple', non-root devices 4) I guess the partitions itself doesn't have to be formated as the filesystem is on the RAID-level. Is that correct? compulsory! I meant, the /dev/mdX has to be formatted, not the individual partitions. Still right? compulsory! if you do anything on the individual components you'll damage data. 5) Removing a disk requires that I do a mdadm -r on all the partitions that is involved in a RAID array. I attempt to by a hot-swap capable controler, so what happens if I just pull out the disk without this manual removal command? as far as md is concerned the disk disappeared. I _think_ this is just like mdadm -r. i think it will be marked faulty, not removed. yep - you're right, I remember now. You have to mdadm -r remove it and re-add it once you restore the disk. So I could actually just pull out the disk, insert a new one and do a mdadm -a /dev/mdX /dev/sdY? The RAID system won't detect the newly inserted disk itself? no, think of it as flexibility. if you want you can build something using the hotplug subsystem. or: no, it would be mighty strange if the raid subsystem just grabbed every new disk it saw... Think of what would happen when I insert my camera's compact flash card and it suddenly gets used as a hot spare grin I'll leave Luca's last word - although it's also worth re-reading Peter's first words!! David one last word: never trust howtos (they should be called howidid), they have the tendency to apply to the author configuration, not yours. general documentation is far more accurate. - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Questions about software RAID
Devid wrote: 5) Removing a disk requires that I do a mdadm -r on all the partitions that is involved in a RAID array. I attempt to by a hot-swap capable controler, so what happens if I just pull out the disk without this manual removal command? as far as md is concerned the disk disappeared. I _think_ this is just like mdadm -r. i think it will be marked faulty, not removed. yep - you're right, I remember now. You have to mdadm -r remove it and re-add it once you restore the disk. First you have to look if there are partitions on that disk to which no data was written since the disk failed (this typically concerns the swap partition). These partitions have to be marked faulty by hand using mdadm -f before you can remove them with mdadm -r. If you have scsi-disks you have to use the following command to take it out off the kernel after removing a faulty disk: echo scsi remove-single-device h.c.i.l /proc/scsi/scsi So I could actually just pull out the disk, insert a new one and do a mdadm -a /dev/mdX /dev/sdY? The RAID system won't detect the newly inserted disk itself? or: no, it would be mighty strange if the raid subsystem just grabbed every new disk it saw... Think of what would happen when I insert my camera's compact flash card and it suddenly gets used as a hot spare grin But if the new disk contains any RAID information and partitions on it then after spinning it up with something like echo scsi add-single-device h.c.i.l /proc/scsi/scsi the RAID system immediately tries to activate those incomming array(s). We had this yesterday on a SuSE 9.3 system. So be carefull walking with used disks from one system to another (this szenario is discussed actually in a parallel thread under topic ... uuid...). no, think of it as flexibility. if you want you can build something using the hotplug subsystem. We tried to build something like a hotplug system :-). Our hardware supports this but in a ratio of 1:10 the kernel (actually 2.6.11-4) crashes when there is activity on that controller while spinning up the new disk. We hoped the system would survive with the remaining (second) controller and the part of the mirrors (RAID1) attached to it but it fails in ca. 10% of our attempts. So till now we weren't lucky to build up a system based on software-raid with no downtime in case of a disk failure. But may be this problem is more related to SCSI than to sw-raid... Bernd Rieke - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Questions about software RAID
David Greaves wrote: Luca Berra wrote: many people find it easier to understand if raid partitions are set to 0XFD. kernel autodetection is broken and should not be relied upon. Could you clarify what is broken? I understood that it was simplistic (ie if you have a raid0 built over a raid5 or something exotic then it may have problems) but essentially worked. Could it be : * broken for complex raid on raid * broken for root devices * fine for 'simple', non-root devices It works when everything works. If something does not work (your disk died, you moved disks, or esp. you added another disk from another machine wich was also a part of (another) raid array), every bad thing can happen, from just inability to assemble the array at all, to using the wrong disks/partitions, and to assembling the wrong array (the one from another machine). If it's your root device you're trying to assemble, recovery involves booting from a rescue CD and cleaning stuff up, which can be problematic at times. /mjt - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Questions about software RAID
On Tue, Apr 19, 2005 at 01:00:11PM +0200, [EMAIL PROTECTED] wrote: You have to mdadm -r remove it and re-add it once you restore the disk. First you have to look if there are partitions on that disk to which no data was written since the disk failed (this typically concerns the swap partition). These partitions have to be marked faulty by hand using mdadm -f before you can remove them with mdadm -r. Ok, but how do you automate/simplify that? A script with a while loop and some grep,sed commands? A grep on what exactly? (this kind of precise information seems to be written nowhere in the manpage of the HOWTOs) Wouldn't it be much simpler if it could be possible to do something like the following? # mdadm --remove-disk /dev/sda So this command could mark as faulty and remove of the array any implied partition(s) of the disk to be removed. Does this currently exist? If not, would you be willing to integrate a patch in that sense? It would be much simpler, don't you think? Same thing for addition... # mdadm --add-disk /dev/sda would do the job quite automatically... Herve -- _ (°= Hervé Eychenne //) Homepage: http://www.eychenne.org/ v_/_ WallFire project: http://www.wallfire.org/ - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Questions about software RAID
Hervé Eychenne wrote: On Tue, Apr 19, 2005 at 01:00:11PM +0200, [EMAIL PROTECTED] wrote: First you have to look if there are partitions on that disk to which no data was written since the disk failed (this typically concerns the swap partition). These partitions have to be marked faulty by hand using mdadm -f before you can remove them with mdadm -r. Ok, but how do you automate/simplify that? EVMS? Or some other enterprise volume manager A script with a while loop and some grep,sed commands? A grep on what exactly? (this kind of precise information seems to be written nowhere in the manpage of the HOWTOs) You're talking about specific configs - not all sysadmins will want to do this. And those who do can type: fdisk -l /dev/sda | grep -i fd | cut -f1 -d' ' | xargs -n1 mdadm -r Wouldn't it be much simpler if it could be possible to do something like the following? # mdadm --remove-disk /dev/sda So this command could mark as faulty and remove of the array any implied partition(s) of the disk to be removed. see above 1 liner... David - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Questions about software RAID
On Tue, Apr 19, 2005 at 04:27:14PM +0100, David Greaves wrote: Hervé Eychenne wrote: On Tue, Apr 19, 2005 at 01:00:11PM +0200, [EMAIL PROTECTED] wrote: First you have to look if there are partitions on that disk to which no data was written since the disk failed (this typically concerns the swap partition). These partitions have to be marked faulty by hand using mdadm -f before you can remove them with mdadm -r. Ok, but how do you automate/simplify that? EVMS? I didn't experience this yet. By I currently have RAID1 setup with mdadm at hand, and I must deal with it... Or some other enterprise volume manager No, thanks. ;-) I prefer taking time to improve free (as a speech) tools than turning to other solutions. A script with a while loop and some grep,sed commands? A grep on what exactly? (this kind of precise information seems to be written nowhere in the manpage of the HOWTOs) You're talking about specific configs - not all sysadmins will want to do this. Of course not all sysadmins will want to do this, but that's not really the question... The question is why not provide something simple to those who want? And those who do can type: fdisk -l /dev/sda | grep -i fd | cut -f1 -d' ' | xargs -n1 mdadm -r I really don't like kludgy things like that... What if the string fd is present in another line? No, that's really ugly, sorry. Ok, maybe you'll come one day with a better command line. But then it will be too complex to remember. So you'll tell me to save it in a script. But that script will stay a bit kludgy anyway and it will not be present on any Linux box. Isn't the insertion/removal of a disk common enough to justify the addition of a simple and clean mdadm option? Herve -- _ (°= Hervé Eychenne //) Homepage: http://www.eychenne.org/ v_/_ WallFire project: http://www.wallfire.org/ - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Questions about software RAID
Hervé Eychenne wrote: And those who do can type: fdisk -l /dev/sda | grep -i fd | cut -f1 -d' ' | xargs -n1 mdadm -r I really don't like kludgy things like that... [...] Isn't the insertion/removal of a disk common enough to justify the addition of a simple and clean mdadm option? have you thought about the idea that there is a certain clue behind the actual behaviour of the mdadm tool? is it so annoying to you to mark a disk/partition as faulty before removing it? do you think it makes sense to implement every single case in an extra command line option? did you ever thought about switching to a hardware where you can remove and add disks without having to do anything else than pull the old one out and push teh new one in? i run several raid arrays on many machines and i find the tools quite useful. if you mind such command lines like the one above you should think about switching to a microsoft product where you can push your mouse arround and tell everyone that you can do what you want without those kludgy command lines which no one really understands. so please ask and learn. there are many people on this list which are pleased to answer your questions. the idea behind *n?x systems is to combine simple functionality through pipes and redirects to gain unlimited complexy and power. so if you want to use the full power of *n?x systems you have to get used to this kludgy command lines. the more you get used to it, the less kludgy they will be. SCNR - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Questions about software RAID
On Tue, Apr 19, 2005 at 06:53:52PM +0200, Frank Wittig wrote: And those who do can type: fdisk -l /dev/sda | grep -i fd | cut -f1 -d' ' | xargs -n1 mdadm -r I really don't like kludgy things like that... [...] Isn't the insertion/removal of a disk common enough to justify the addition of a simple and clean mdadm option? have you thought about the idea that there is a certain clue behind the actual behaviour of the mdadm tool? is it so annoying to you to mark a disk/partition as faulty before removing it? I'm sorry, but having to do a cat /proc/mdstat, figure out by myself what to do (which partition is concerned), then type several commands (for each concerned partition) actually is painful. Maybe you are an experienced guy so it seems so simple to you... but I'm always amused when an experienced guy refuses to make things simpler for those who aren't as much as he is. And sends them to Microsoft. Great. This mailing-list is probably full of kernel guys, so maybe I should have guessed. But I come here as a user (who wants RAID to work as smoothly as possible), having found no other mailing-list (a user one) for RAID on Linux. (did I miss it?) Maybe I'm not asking questions to the right people, but for me, computer science is about automating things. And the process or replacing a crashed disk (described above) on a system managed with mdadm is not particularly automated, right? Maybe it's not a problem for _you_, because you know exactly what to do by heart. So you've forgotten the complexity. But it's there, and even if it's good that you can do complex and powerful things, it's not normal to force people to get into that complexity to do simple things. Think about it. do you think it makes sense to implement every single case in an extra command line option? I personnaly do not consider that this is yet another case. For me, RAID is about have disk availability, right? So the most common production case is definitely when one of your disks crashed, and you want to replace it. There must be some kind of way to deal with that without typing too much contextual command lines. Whether this simple way should belong to mdadm is another question, but I personnaly think it should, as it would introduce no overhead (would it, really ?) and would be very helpful. Let me reassure you, you could stay with several commands if you like. :-) did you ever thought about switching to a hardware where you can remove and add disks without having to do anything else than pull the old one out and push teh new one in? Ok, here we are... [First, the RAID controller I'm forced to deal with has no Linux driver, but that's not important for our discussion.] Software RAID is about doing the same that hardware RAID, but in soft. I think we agree on that. ;-) So I see absolutely no reason why software RAID should not be as simple as possible. And RAID management with mdadm could be made simpler for a common case like that. i run several raid arrays on many machines and i find the tools quite useful. They are. They could be even more if things were as simple as possible. if you mind such command lines like the one above you should think about switching to a microsoft product where you can push your mouse arround and tell everyone that you can do what you want without those kludgy command lines which no one really understands. so please ask and learn. You tell me to ask and learn from kernel guys who like to type command lines (I do, but I don't want to force everyone to do so). So maybe I can tell you to please learn from users who like the command line, but try to make simple things as simple as possible. there are many people on this list which are pleased to answer your questions. the idea behind *n?x systems is to combine simple functionality through pipes and redirects to gain unlimited complexy and power. so if you want to use the full power of *n?x systems you have to get used to this kludgy command lines. I don't agree with that. Using grep on vague patterns is not what I call power. Having to type several commands when one would be enough (I insist that I think we are talking about one of the most common cases) is not powerful, according to me. My motto is be as complex as possible for people who want power (you, and sometimes me), but be as simple as possible for people who just want things to be done quickly, simply, and efficiently (sometimes me, and all the others). the more you get used to it, the less kludgy they will be. Of course, but the very idea is that one shouldn't have to get used to it too much to perform simple and common actions. But I guess we'll never agree anyway... :-( Herve -- _ (°= Hervé Eychenne //) Homepage: http://www.eychenne.org/ v_/_ WallFire project: http://www.wallfire.org/ - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at
Re: Questions about software RAID
Hervé Eychenne wrote: Maybe you are an experienced guy so it seems so simple to you... but I'm always amused when an experienced guy refuses to make things simpler for those who aren't as much as he is. And sends them to Microsoft. Great. i don't send you to microsoft. i want you to understand the philosophy behind linux. the sort of functionality you want doesn't belong to the mdadm tool. mdadm is the command line interface to dm. more complex functionality like the one you desire is covered by frontends like EVMS. i don't know EVMS but what i heard about it sounds exactly like what you want. simple administration without having to know how things work in the background. I personnaly do not consider that this is yet another case. For me, RAID is about have disk availability, right? So the most common production case is definitely when one of your disks crashed, and you want to replace it. There must be some kind of way to deal with that without typing too much contextual command lines. after the first time you lose data because of a failure of an automated process you will think different about that. i think automation is fine for normal operation. failure of a component is far from normal and in this case full control is what you want/need. Whether this simple way should belong to mdadm is another question, but I personnaly think it should, as it would introduce no overhead (would it, really ?) and would be very helpful. KISS: keep it stupid simple this is the philosophy. keep low-level tools stupid simple. more complexity brings a higher risk of failure. we're talking about raid. not about doing backups or syncing the system clock. did you ever thought about switching to a hardware where you can remove and add disks without having to do anything else than pull the old one out and push teh new one in? Ok, here we are... [First, the RAID controller I'm forced to deal with has no Linux driver, but that's not important for our discussion.] there are some nice boxes arround. ther take a bunch of disks and appear to the host as a simple SCSI disk. had such a thing in the past. replacing disks was so simple a secretary could have done that. ;-) I don't agree with that. Using grep on vague patterns is not i think grep is far more powerfull as you think. the more you get used to it, the less kludgy they will be. Of course, but the very idea is that one shouldn't have to get used to it too much to perform simple and common actions. if replacing disks is a common case to you, you should buy your disks from a different manufacturer. ;-) and if you have so many arrays that a disk failure is common because of the number of disks, you would want to know the basics. But I guess we'll never agree anyway... :-( we're just on different levels of usage. and there's a tool for everyone on us. my tool is mdadm. and yours is EVMS or some other high level frontend which abstracts the use of the low-level tools behind a nice looking UI. greetings, Frank - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
RE: Questions about software RAID
-Original Message- From: [EMAIL PROTECTED] [mailto:linux-raid- [EMAIL PROTECTED] On Behalf Of Frank Wittig Sent: Tuesday, April 19, 2005 3:47 PM To: [EMAIL PROTECTED] Cc: linux-raid@vger.kernel.org Subject: Re: Questions about software RAID Hervé Eychenne wrote: Maybe you are an experienced guy so it seems so simple to you... but I'm always amused when an experienced guy refuses to make things simpler for those who aren't as much as he is. And sends them to Microsoft. Great. i don't send you to microsoft. i want you to understand the philosophy behind linux. the sort of functionality you want doesn't belong to the mdadm tool. mdadm is the command line interface to dm. more complex functionality like the one you desire is covered by frontends like EVMS. i don't know EVMS but what i heard about it sounds exactly like what you want. simple administration without having to know how things work in the background. I personnaly do not consider that this is yet another case. For me, RAID is about have disk availability, right? So the most common production case is definitely when one of your disks crashed, and you want to replace it. There must be some kind of way to deal with that without typing too much contextual command lines. after the first time you lose data because of a failure of an automated process you will think different about that. i think automation is fine for normal operation. failure of a component is far from normal and in this case full control is what you want/need. Whether this simple way should belong to mdadm is another question, but I personnaly think it should, as it would introduce no overhead (would it, really ?) and would be very helpful. KISS: keep it stupid simple this is the philosophy. keep low-level tools stupid simple. more complexity brings a higher risk of failure. we're talking about raid. not about doing backups or syncing the system clock. did you ever thought about switching to a hardware where you can remove and add disks without having to do anything else than pull the old one out and push teh new one in? Ok, here we are... [First, the RAID controller I'm forced to deal with has no Linux driver, but that's not important for our discussion.] there are some nice boxes arround. ther take a bunch of disks and appear to the host as a simple SCSI disk. had such a thing in the past. replacing disks was so simple a secretary could have done that. ;-) I don't agree with that. Using grep on vague patterns is not i think grep is far more powerfull as you think. the more you get used to it, the less kludgy they will be. Of course, but the very idea is that one shouldn't have to get used to it too much to perform simple and common actions. if replacing disks is a common case to you, you should buy your disks from a different manufacturer. ;-) and if you have so many arrays that a disk failure is common because of the number of disks, you would want to know the basics. But I guess we'll never agree anyway... :-( we're just on different levels of usage. and there's a tool for everyone on us. my tool is mdadm. and yours is EVMS or some other high level frontend which abstracts the use of the low-level tools behind a nice looking UI. greetings, Frank Well, I agree with KISS, but from the operator's point of view! I want the failed disk to light a red LED. I want the tray the disk is in to light a red LED. I want the cabinet the tray is in to light a red LED. I want the re-build to the spare to start. I want the operator du jour to notice the red LEDs. I want the operator to remove the failed disk. I want the operator to install the new disk. I want the re-build to the new disk to start. I want the re-build to not fail the current spare so data says redundant. I want the old spare to become the spare again. (optional) The operator would log the event: Disk xyz's LED went red, I replaced the disk, the red LED went out. In my opinion, most operators would not be able to replace a disk on a md RAID system. It is much too complex! Most operators need written procedures. They can't use independent thought to resolve problems. Also, most operators can't use vi! So, if you can use vi, you are better than most operators!!! IMO. Of course I can't have the red LED, but the disks could be labeled and an email sent saying disk xyz has failed. The operator could then replace disk xyz, if they could find it! Then another email(s) with a status update. With most (maybe all) hardware RAID systems I have used, the above is how it works. Even the red LED!!! But these are dedicated RAID systems, not off the shelf components. I don't expect a software solution to ever be as easy as hardware, but I do agree it needs to be much more operator friendly than it is today. Guy - To unsubscribe from this list: send the line unsubscribe linux-raid in the body
RE: Questions about software RAID - red led
On Wed, 20 Apr 2005, Guy wrote: Well, I agree with KISS, but from the operator's point of view! I want the failed disk to light a red LED. I want the tray the disk is in to light a red LED. I want the cabinet the tray is in to light a red LED. I want the re-build to the spare to start. I want the operator du jour to notice the red LEDs. I want the operator to remove the failed disk. I want the operator to install the new disk. I want the re-build to the new disk to start. I want the re-build to not fail the current spare so data says redundant. I want the old spare to become the spare again. (optional) The operator would log the event: Disk xyz's LED went red, I replaced the disk, the red LED went out. In my opinion, most operators would not be able to replace a disk on a md RAID system. It is much too complex! Most operators need written procedures. They can't use independent thought to resolve problems. if you want the above ... it is possible to do ... its just a few hardware tweeking on the drive tray ... ( trivial to do if you have access to the ide disk tray and backplane ) operator du jour does NOT need to do anyting ... software raid can detect or be told that a disk went bad and it will rebuild itself after the drive tray is removed and replaced with the same disk or different disk - think usb .. you plug it in .. it comes up - think cdrom .. you put it in .. it comes up - think new disk tray .. you plug it in .. it comes up - the bigger problem .. - disks should NOT be dying in the first place and yup.. building customizations is the fun part c ya alvin - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Questions about software RAID
tmp wrote: I read the software RAID-HOWTO, but the below 6 questions is still unclear. I have asked around on IRC-channels and it seems that I am not the only one being confused. Maybe the HOWTO could be updated to clearify the below items? 1) I have a RAID-1 setup with one spare disk. A disk crashes and the spare disk takes over. Now, when the crashed disk is replaced with a new one, what is then happening with the role of the spare disk? the new disk is spare, the array doesn't revert to it's original state. Is it reverting to its old role as spare disk? so no it doesn't. If it is NOT reverting to it's old role, then the raidtab file will suddenly be out-of-sync with reality. Is that correct? yes raidtab is deprecated - man mdadm Does the answer given here differ in e.g. RAID-5 setups? no 2) The new disk has to be manually partitioned before beeing used in the array. no it doesn't. You could use the whole disk (/dev/hdb). In general, AFAIK, partitions are better as they allow automatic assembly at boot. What happens if the new partitions are larger than other partitions used in the array? nothing special - eventually, if you replace all the partitions with bigger ones you can 'grow' the array What happens if they are smaller? it won't work (doh!) 3) Must all partition types be 0xFD? What happens if they are not? no They won't be autodetected by the _kernel_ 4) I guess the partitions itself doesn't have to be formated as the filesystem is on the RAID-level. Is that correct? compulsory! 5) Removing a disk requires that I do a mdadm -r on all the partitions that is involved in a RAID array. I attempt to by a hot-swap capable controler, so what happens if I just pull out the disk without this manual removal command? as far as md is concerned the disk disappeared. I _think_ this is just like mdadm -r. Aren't there some more hotswap-friendly setup? What's unfriendly? 6) I know that the kernel does stripping automatically if more partitions are given as swap partitions in /etc/fstab. But can it also handle if one disk crashes? no - striping mirroring The kernel will fail to read data on the crashed disk - game over. I.e. do I have to let my swap disk be a RAID-setup too if I wan't it to continue upon disk crash? yes - a mirror, not a stripe. David - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Questions about software RAID
Thanks for your answers! They led to a couple of new questions, however. :-) I've read man mdadm and man mdadm.conf but I certainly doesn't have an overview of software RAID. yes raidtab is deprecated - man mdadm OK. The HOWTO describes mostly a raidtools context, however. Is the following correct then? mdadm.conf may be considered as the replacement for raidtab. When mdadm starts it consults this file and starts the raid arrays correspondingly. This leads to the following: a) If mdadm starts the arrays, how can I then boot from a RAID device (mdadm isn't started upon boot)? I don't quite get which parts of the RAID system are controled by the kernel and which parts are controled by mdadm. b) Whenever I replace disks, the runtime configuration changes. I assume that I should manually edit mdadm.conf in order to make corespond to reality? 2) The new disk has to be manually partitioned before beeing used in the array. no it doesn't. You could use the whole disk (/dev/hdb). In general, AFAIK, partitions are better as they allow automatic assembly at boot. Is it correct that I can use whole disks (/dev/hdb) only if I make a partitionable array and thus creates the partitions UPON the raid mechanism? As far as I can see, partitionable arrays makes disk replacements easier as you can just replace the disk and let the RAID software take care of syncing the new disk with existing partitioning. Is that correct? You say I can't boot from such a partitionable raid array. Is that correctly understood? Can I grow a partitionable raid array if I replace the existing disks with larger ones later? Would you prefer manual partitioned disks, even though disk replacements are a bit more difficult? I guess that mdadm automatically writes persistent superblocks to all disks? 3) Must all partition types be 0xFD? What happens if they are not? no They won't be autodetected by the _kernel_ OK, so it is generally a good idea to always set the partition types to 0xFD, I guess. 4) I guess the partitions itself doesn't have to be formated as the filesystem is on the RAID-level. Is that correct? compulsory! I meant, the /dev/mdX has to be formatted, not the individual partitions. Still right? 5) Removing a disk requires that I do a mdadm -r on all the partitions that is involved in a RAID array. I attempt to by a hot-swap capable controler, so what happens if I just pull out the disk without this manual removal command? as far as md is concerned the disk disappeared. I _think_ this is just like mdadm -r. So I could actually just pull out the disk, insert a new one and do a mdadm -a /dev/mdX /dev/sdY? The RAID system won't detect the newly inserted disk itself? I.e. do I have to let my swap disk be a RAID-setup too if I wan't it to continue upon disk crash? yes - a mirror, not a stripe. OK. Depending on your recomendations above, I could either make it a swap partition on a partitionable array or create an array for the swap in the conventional way (of existing partitions). Thanks again for your help! Are there some HOWTO out there, that is up-to-date and is based on RAID usage with mdadm and kernel 2.6 instead of raidtools and kernel 2.2/2.4? I can't possibly be the only one with these newbie questions. :-) - To unsubscribe from this list: send the line unsubscribe linux-raid in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
