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Re: XFS + SMP + Software RAID 5 slow?

To: "Andrew Klaassen" <ak@xxxxxxx>
Subject: Re: XFS + SMP + Software RAID 5 slow?
From: "Simon Matter" <simon.matter@xxxxxxxxxxxxxxxx>
Date: Sat, 1 Nov 2003 00:14:45 +0100 (CET)
Cc: linux-xfs@xxxxxxxxxxx
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> 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.  Obviously there's something very
>> wrong here.
>> Known issue?  Any idea what might be causing this?
> By the way: Using hardware RAID 5 on exactly the same setup, the
> XFS and EXT3 numbers are virtually identical (~5MB/sec sustained
> write).  Only software RAID 5 seems to cause this great
> divergence.

Did you try your setup with an external log? IIRC the problem with bad
write performance on software RAID 5 should have been adressed and mostly
fixed with the XFS1.3.x release. I recommend to try with external log
anyway. I never had good results on my software RAID 5 configurations
until I used external log. However, I never did my tests again in the
XFS1.3.x days.


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