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Re: XFS over LVM over md RAID

To: xfs@xxxxxxxxxxx
Subject: Re: XFS over LVM over md RAID
From: Michael Monnerie <michael.monnerie@xxxxxxxxxxxxxxxxxxx>
Date: Fri, 10 Sep 2010 02:25:55 +0200
Cc: Richard Scobie <richard@xxxxxxxxxxx>
In-reply-to: <4C89668E.6010800@xxxxxxxxxxx>
Organization: it-management http://it-management.at
References: <4C89668E.6010800@xxxxxxxxxxx>
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On Freitag, 10. September 2010 Richard Scobie wrote:
> Limited testing using dd and bonnie++ shows no difference in write 
> performance
 
For dd it should always show the same, as you just sequentially write a 
large file. Only with bonnie you would see differences due to stripe 
sets, as the speed only drops when doing I/O not on boundaries and/or 
smaller than the stripe size, as the stripe size is the smallest 
possible I/O for the RAID.

I don't know why you don't see any difference with bonnie though.

FWIW, a stripe set of 256k means you do read/write 256k from a single 
drive on each I/O, then the next 256k from the next drive. I hope you 
have very few small accesses and mostly very large files. If you'd use a 
database on that system it would crawl...

-- 
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Michael Monnerie, Ing. BSc

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