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Re: Disappointing performance of copy (MD raid + XFS)

To: Kasper Sandberg <postmaster@xxxxxxxxxxx>
Subject: Re: Disappointing performance of copy (MD raid + XFS)
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Tue, 15 Dec 2009 10:53:23 -0600
Cc: Dave Chinner <david@xxxxxxxxxxxxx>, Asdo <asdo@xxxxxxxxxxxxx>, linux-raid <linux-raid@xxxxxxxxxxxxxxx>, Kristleifur Daðason <kristleifur@xxxxxxxxx>, Gabor Gombas <gombasg@xxxxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <1260895872.7209.46.camel@localhost>
References: <4B204334.1000605@xxxxxxxxxxxxx> <4B207620.3060605@xxxxxxxxxxx> <4B21A34C.9090100@xxxxxxxxxxxxx> <20091211032610.GH30608@xxxxxxxxxxxxxxxx> <1260895872.7209.46.camel@localhost>
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Kasper Sandberg wrote:
> On Fri, 2009-12-11 at 14:26 +1100, Dave Chinner wrote:
>> On Fri, Dec 11, 2009 at 02:41:32AM +0100, Asdo wrote:
>>> I have checked the other problem I had which I was mentioning, that I  
> <snip>
>>> Also with noalign and rotorstep at 255 the stripe_cache_size stays  
>>> usually in the lower half (below 16000 out of 32000) while with defaults  
>>> it's stuck for most of the time at the maximum and processes are stuck  
>>> sleeping in MD locks for this reason.
>> That really does sound like a misaligned filesystem - the stripe
>> cache will grow larger the more RMW cycles that need to be
>> performed...
> Sorry to interrupt, I would very much like to see if my array/xfs is
> properly aligned and all that stuff which has been mentioned inhere,
> could any of you please post the things required to check? filesystem is
> straight on md raid6, debian lenny.
> <snip>

use xfs_info on your mountpoint, and compare the stripe unit and width
to what md tells you.  xfs_info stripe unit/width output is in fs blocks


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