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Re: Strange fragmentation in nearly empty filesystem

To: Carsten Oberscheid <oberscheid@xxxxxxxxxxxx>
Subject: Re: Strange fragmentation in nearly empty filesystem
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Fri, 23 Jan 2009 09:25:27 -0600
Cc: xfs@xxxxxxxxxxx
In-reply-to: <20090123102130.GB8012@xxxxxxxxxxxx>
References: <20090123102130.GB8012@xxxxxxxxxxxx>
User-agent: Thunderbird 2.0.0.19 (Macintosh/20081209)
Carsten Oberscheid wrote:
> Hi there,
> 
> I am experiencing my XFS filesystem degrading over time in quite a
> strange and annoying way. Googling "XFS fragmenation" tells me either
> that this does not happen or to use xfs_fsr, which doesn't really help
> me anymore -- see below. I'd appreciate any help on this.
> 
> Background: I am using two VMware virtual machines on my Linux
> desktop. These virtual machines store images of their main memory in
> .vmem files, which are about half a gigabyte in size for each of my
> VMs. The .vmem files are created when starting the VM, written when
> suspending it and read when resuming. I prefer suspendig and resuming
> over shutting down and booting again, so with my VMs these files can
> have a lifetime of several weeks.

I would suggest using xfs_bmap to look at the file layout, it will be
much more informative than filefrag.

I don't know how vmware is writing the files out (I don't use vmware, so
can't test) but I'd suggest looking at xfs_bmap output when it's first
created, and then also when it's first written (but perhaps before it
gets too horribly fragmented).

The first question I'd ask is whether it's a swiss-cheese looking sparse
file with many holes.

-Eric

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