[CentOS] disk I/O problems with LSI Logic RAID controller

[Fernando Gleiser]

----- 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