From: Spelic <spelic@shiftmail.org>
To: xfs@oss.sgi.com
Subject: Re: Verify filesystem is aligned to stripes
Date: Fri, 26 Nov 2010 14:15:35 +0100 [thread overview]
Message-ID: <4CEFB2F7.5070103@shiftmail.org> (raw)
In-Reply-To: <20101126122218.GH12187@dastard>
On 11/26/2010 01:22 PM, Dave Chinner wrote:
>
> FWIW, for workloads that do random, small IO, XFS works best when you
> _turn off_ aligned allocation and just let it spray the IO at the
> disks. This works best if you are using RAID 0/1/10. All the numbers
> I've been posting are with aligned allocation turned off (i.e. no
> sunit/swidth set).
>
I think I also noticed this...
The thing is, for large sequential I/O it seems to me it's indifferent
if XFS is aligned or not, because the resulting file will anyway be
sequential, and if you have raid10 or even parity raid with a large
stripe cache there won't be any reads anyway. Ok maybe with alignment
you could avoid reads on the first stripe (not sure, it might read
anyway if the RAID reacts fast, before enough output is sent to it), but
that's the only one.
So when is alignment to be turned on?
Thanks for the info
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next prev parent reply other threads:[~2010-11-26 13:12 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-11-24 18:39 Verify filesystem is aligned to stripes Spelic
2010-11-25 5:46 ` Dave Chinner
2010-11-25 7:00 ` Stan Hoeppner
2010-11-25 10:15 ` Dave Chinner
2010-11-25 22:57 ` Stan Hoeppner
2010-11-26 8:16 ` Emmanuel Florac
2010-11-26 12:22 ` Dave Chinner
2010-11-26 13:15 ` Spelic [this message]
2010-11-26 14:05 ` Michael Monnerie
2010-11-26 14:36 ` Emmanuel Florac
-- strict thread matches above, loose matches on Subject: below --
2010-11-26 2:43 Richard Scobie
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