perc 4 write performance after upgrading to debian lenny

Brice Figureau brice+dell at daysofwonder.com
Fri Jul 17 09:32:22 CDT 2009


On Thu, 2009-07-16 at 08:01 -0500, Matthew Lenz wrote:
> On Thu, 2009-07-16 at 07:56 -0500, Rayford_Johnson at Dell.com wrote:
> > >  -----Original Message-----
> > >  From: linux-poweredge-bounces at lists.us.dell.com 
> > >  [mailto:linux-poweredge-bounces at lists.us.dell.com] On Behalf 
> > >  Of Matthew Lenz
> > >  Sent: Thursday, July 16, 2009 7:44 AM
> > >  To: linux-poweredge-Lists
> > >  Subject: Re: perc 4 write performance after upgrading to debian lenny
> > >  
> > >  On Mon, 2009-07-13 at 11:04 -0500, Matthew Lenz wrote:
> > >  > [    8.791408] sd 0:2:0:0: [sda] Write Protect is off
> > >  > [    8.791412] sd 0:2:0:0: [sda] Mode Sense: 00 00 00 00
> > >  > [    8.791432] sd 0:2:0:0: [sda] Asking for cache data failed
> > >  > [    8.791480] sd 0:2:0:0: [sda] Assuming drive cache: 
> > >  write through
> > >  > 
> > >  anyone able to provide some insight on this one?  its really hosing
> > >  things up :(
> > >  
> > 
> > This message displays when the Linux SCSI Mid Layer asks for physical
> > disk cache settings. Because the PERC firmware manages the virtual disk
> > cache settings on a per controller and a per virtual disk basis, the
> > firmware does not respond to this command. Thus, the Linux SCSI Mid
> > Layer assumes that the virtual disk's cache policy is write through
> > since it is the safer choice.
> > 
> > Except for this message, there is no side effect to this behavior. The
> > cache policy of the virtual disk and the I/O throughput are not affected
> > by this message. The cache policy settings for the PERC remain the
> > settings chosen for a given virtual disk. 
> > 
> > http://lists.us.dell.com/fom-serve/cache/110.html
> 
> Thanks so much for pointing that out.  Any ideas on how to proceed
> diagnosing the poor performance?  Is there a benchmark I can post to the
> list for the boxes to help accurately determine what exactly my read /
> write performance is?

I can't remember what kernel sarge had, but lenny is shipped with
2.6.26, so
I'm wondering if you're not seeing those various never ending bugs which
don't have a solution:
http://bugzilla.kernel.org/show_bug.cgi?id=7372
http://bugzilla.kernel.org/show_bug.cgi?id=12309
https://bugzilla.redhat.com/show_bug.cgi?id=470736
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/131094

I suggest you experiment with the various tips included in each bug
reports, and also try new kernels (2.6.30 is in sid, combined with ext4
for instance might really help).

Good luck,
-- 
Brice Figureau
My Blog: http://www.masterzen.fr/



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