----- Original Message ----
From: Ross Walker rswwalker@gmail.com To: CentOS mailing list centos@centos.org Cc: CentOS mailing list centos@centos.org Sent: Thu, February 11, 2010 12:30:43 PM Subject: Re: [CentOS] disk I/O problems with LSI Logic RAID controller
On Feb 11, 2010, at 2:46 AM, Andrzej Szymanski wrote:
The iostat output looks good to me for the RAID setup you have. I'd look for the problem in a different place:
note the output of cat /proc/sys/vm/dirty_background_ratio and try echo 1 > /proc/sys/vm/dirty_background_ratio whether it helps.
Excellent suggestion, on machines with lots of memory the default dirty background ratio is way too big, and needs to be tuned down for both data integrity in the event of a system failure and performance of the underlying storage configuration.
Take into account the RAID setup, write-back cache size and time it takes to empty it to disk and pick a dirty background ratio somewhere in between.
You nailed it. I tweaked the dirty_background ratio and changed the scheduller to deadline and now it works way better. it still see-saws a bit but the utilization never dropts to zero.
Thanks you for your help.
Fer