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Re: Poor VMWare disk performance on XFS partition

To: Eric Sandeen <sandeen@xxxxxxxxxxx>
Subject: Re: Poor VMWare disk performance on XFS partition
From: Andi Kleen <andi@xxxxxxxxxxxxxx>
Date: 24 Mar 2008 05:02:04 +0100
Cc: "Hendrik ." <chasake@xxxxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <47E6C09E.5030601@sandeen.net>
References: <876423.51989.qm@web52006.mail.re2.yahoo.com> <47E6C09E.5030601@sandeen.net>
Sender: xfs-bounce@xxxxxxxxxxx
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Eric Sandeen <sandeen@xxxxxxxxxxx> writes:
> 
> What does xfs_bmap and/or filefrag say, is this file indeed very
> fragmented?  

> And is it less so on ext3?  If the file is persistent then
> preallocating it would probably help.

Preallocating would prevent one of the main features of 
a sparse VM images: starting small and only growing as the
virtual machine needs more storage without having to
resize the virtual partitions.

I remember XFS had a mmap problem a long time ago (in 2.4) which
sounded similar (iirc it trickered with samba), but I thought
it was long fixed. The problem back then was that page
flushing on mmaps didn't get merged due to some unfortunate VM
interactions and then thousands of extents got created on flushing
a mmap. A lot of extents seems to make XFS slow.

-Andi


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