----- Original Message ---- > From: Ross Walker <rswwalker at gmail.com> > To: CentOS mailing list <centos at centos.org> > Cc: CentOS mailing list <centos at 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