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]
