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Re: XFS + SMP + Software RAID 5 slow?

To: linux-xfs@xxxxxxxxxxx
Subject: Re: XFS + SMP + Software RAID 5 slow?
From: Andrew Klaassen <ak@xxxxxxx>
Date: Fri, 31 Oct 2003 18:19:43 -0500
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Responding to myself again, with more details...

On Fri, Oct 31, 2003 at 04:50:13PM -0500,
Andrew Klaassen wrote:

> I've been experiencing *very* slow sustained write ( < .5MB/sec)
> using 2.4.20-20.9.XFS1.3.1smp on a dual-Xeon box with a 3ware
> 7506 card in JBOD mode.  Software RAID 5.  No such problems with
> Ext3 ( > 20MB/sec sustained write) with the same kernel on the
> same software RAID 5 device.

I got those results using fs-bench:

http://h2np.net/tools/fs-bench.tar.gz

...using a little python script that simply monitors df -k. 
Bonnie++ gives very different results; still favouring Ext3, but
the XFS results are at least acceptable:

Ext3:
Version  1.03       ------Sequential Output------ --Sequential Input- --Random-
                    -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
thor.dkp.com 10000M           42713  44 33594  29           140724  49 215.5   1

XFS:
Version  1.03       ------Sequential Output------ --Sequential Input- --Random-
                    -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
thor.dkp.com 10000M           20418  11 29688  16           134639  45 235.0   1

Hmm... so:

Would there either be 1) something about fs-bench that would
cause XFS to perform poorly or 2) something about watching df -k
with XFS that gives misleading results?

If anyone else could try fs-bench on an XFS-over-software-RAID5
setup and let me know their results, I'd be much obliged.

Andrew Klaassen


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