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Re: 30 TB RAID6 + XFS slow write performance

To: xfs@xxxxxxxxxxx
Subject: Re: 30 TB RAID6 + XFS slow write performance
From: Michael Monnerie <michael.monnerie@xxxxxxxxxxxxxxxxxxx>
Date: Wed, 20 Jul 2011 16:04:31 +0200
Cc: Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>, Dave Chinner <david@xxxxxxxxxxxxx>, John Bokma <contact@xxxxxxxxxxxxx>
In-reply-to: <4E26C5C5.1090802@xxxxxxxxxxxxxxxxx>
Organization: it-management http://it-management.at
References: <4E24907F.6020903@xxxxxxxxxxxxx> <20110720064419.GG9359@dastard> <4E26C5C5.1090802@xxxxxxxxxxxxxxxxx>
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On Mittwoch, 20. Juli 2011 Stan Hoeppner wrote:
> I thought this was packing multiple small files into
> a single stripe write, which you just explained XFS does not do.

This is interesting, I jump in here. Does that mean that if I have a XFS 
volume with sw=14,su=64k (14*64=896KiB) that when I write 10 small files 
in the same dir with 2KB each, each file would be placed at a 896KiB 
boundary? That way, all stripes of a 1GB partition would be full when 
there are roughly 1170 files (1170*896KiB ~ 1GB). What would happen when 
I create other files - is XFS "full" then, or would it start using sub-
stripes? If sub-stripes, would they start at su (=64KiB) distances, or 
at single block (e.g. 4KiB) distances?

I hope I could explain my thoughts in an understandable way ;-)

mit freundlichen Grüssen,
Michael Monnerie, Ing. BSc

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