Re: RAID 5 performance issue.

["John Stoffel" <john@stoffel.org>]

>>>>> "Andrew" == Andrew Clayton <andrew@digital-domain.net> writes:

Andrew> On Thu, 4 Oct 2007 10:10:02 -0400 (EDT), Justin Piszcz wrote:


>> Also, did performance just go to crap one day or was it gradual?

Andrew> IIRC I just noticed one day that firefox and vim was
Andrew> stalling. That was back in February/March I think. At the time
Andrew> the server was running a 2.6.18 kernel, since then I've tried
Andrew> a few kernels in between that and currently 2.6.23-rc9

Andrew> Something seems to be periodically causing a lot of activity
Andrew> that max's out the stripe_cache for a few seconds (when I was
Andrew> trying to look with blktrace, it seemed pdflush was doing a
Andrew> lot of activity during this time).
 
Andrew> What I had noticed just recently was when I was the only one
Andrew> doing IO on the server (no NFS running and I was logged in at
Andrew> the console) even just patching the kernel was crawling to a
Andrew> halt.

How much memory does this system have?  Have you checked the output of
/proc/mtrr at all?  There' have been reports of systems with a bad
BIOS that gets the memory map wrong, causing access to memory to slow
down drastically.

So if you have 2gb of RAM, try booting with mem=1900m or something
like that and seeing if things are better for you.

Make sure your BIOS is upto the latest level as well.

John