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Re: XFS defragmentation issue

To: John Lister <john.lister@xxxxxxxxxxxxx>
Subject: Re: XFS defragmentation issue
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Sat, 11 Sep 2010 18:23:30 +1000
Cc: xfs@xxxxxxxxxxx
In-reply-to: <4C8B27E4.2050102@xxxxxxxxxxxxx>
References: <4C8A4395.5070702@xxxxxxxxxxxxx> <4C8B27E4.2050102@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
On Sat, Sep 11, 2010 at 07:55:32AM +0100, John Lister wrote:
>  Stan Hoeppner wrote on 9/10/2010 14:00
> >>On 10/09/2010 15:41, John Lister wrote:
> >Try unmounting and remounting the filesystem, and see if the various
> >tools all report the same thing afterwards. This solved the exact same
> >problem for me very recently, though I'm on kernel and xfsprogs
> >2.9.8.
> Cheers, that got rid of most of it, there is still a slight
> discrepency  (50 extra fragments) which I can live with.

xfs_db used buffered IO on the block device, which is not coherent
with the filesystem. If you are using it on an active filesystem,
then running "echo 1 > /proc/sys/vm/drop_caches" before you run
xfs_db should make it read from disk at least once....


Dave Chinner

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