Subject: Re: poor io performance with xfs+raid5
From: Steve Lord <lord@sgi.com>
To: Mike Eldridge <diz@cafes.net>
Cc: Simon Matter <simon.matter@ch.sauter-bc.com>,
   Justin Coffey
	 <justin@homes.com>, linux-xfs@oss.sgi.com
In-Reply-To: <20020425144025.N16048@ornery.cafes.net>
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	<3CC85999.501431E5@ch.sauter-bc.com> 
	<20020425144025.N16048@ornery.cafes.net>
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Date: 25 Apr 2002 15:19:05 -0500
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On Thu, 2002-04-25 at 14:40, Mike Eldridge wrote:
> On Thu, Apr 25, 2002 at 09:31:37PM +0200, Simon Matter wrote:
> > 
> > Hi,
> > 
> > Hardware RAID is not affected at all. All levels of Software RAID beside
> > RAID5 are okay. The only problem is with Software RAID5 and internal
> > log. Under some circumstances, this config can slow down performance
> > _dramatically_.
> 
> it should be noted that i am using hardware raid5:
> 
> > > > > the system is configured as such:
> > > > >     60GB RAID5 (escalade 7850 + 4x20GB IBM deskstar) mounted on /var
> > > > >     log=internal,bsize=4096,blocks=1839
> > > > >     agcount=58,agsize=262144 blocks
> > > > >     realtime=none
> 
> via a 3ware escalade 7850 ata-raid card.
> 

Well, Duh! I should have seen that first time around, I get into the
habit of reading my email too fast!

We may be able to fix some things, if we can remake the filesystem.
First you need to know the stripe unit of your raid - we can feed
this into XFS to make it do stripe aligned allocations. This has
to be done by hand on linux. Take a look at the mkfs.xfs man page
and the section on sunit and swidth options. Probably bump your log size
up from the default somewhat, not sure how it ended up as 1839
that is scary.

You still have not said which kernel version you are running beyond 2.4,
unless I speed read over that too.

Steve


-- 

Steve Lord                                      voice: +1-651-683-3511
Principal Engineer, Filesystem Software         email: lord@sgi.com