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Re: Strange fragmentation in nearly empty filesystem

To: xfs@xxxxxxxxxxx
Subject: Re: Strange fragmentation in nearly empty filesystem
From: Carsten Oberscheid <oberscheid@xxxxxxxxxxxx>
Date: Tue, 27 Jan 2009 15:37:24 +0100
In-reply-to: <497F0C78.7060501@xxxxxxxxxxx>
References: <20090123102130.GB8012@xxxxxxxxxxxx> <20090124003329.GE32390@disturbed> <20090126075724.GA1753@xxxxxxxxxxxx> <497E02CD.2020000@xxxxxxxxxxx> <20090127071023.GA16511@xxxxxxxxxxxx> <20090127084034.GA16931@xxxxxxxxxxxx> <497F0C78.7060501@xxxxxxxxxxx>
User-agent: Mutt/1.5.13 (2006-08-11)
On Tue, Jan 27, 2009 at 07:30:32AM -0600, Eric Sandeen wrote:
> It'd be best to run vmware under some other kernel, and observe its
> behavior, not just mount some existing filesystem and look at existing
> files and do other non-vmware-related tests.

If this really is just a vmware and/or kernel problem that has nothing
to do with the filesystem, then I agree.

> You went from a file with 34 holes to one with 27k holes by copying it?


>  Perhaps this is cp's sparse file detection in action, seeking over
> swaths of zeros.
> Perhaps, if by "worse" you mean "leaves holes for regions with zeros".
> Try cp --sparse=never and see how that goes.

Didn't know this one.

[co@tangchai]~/vmware/foo cp --sparse=never foo.vmem test_nosparse

[co@tangchai]~/vmware/foo xfs_bmap -vvp test_ | grep hole | wc -l
test_livecd    test_nosparse  

[co@tangchai]~/vmware/foo xfs_bmap -vvp test_nosparse | grep hole | wc -l

[co@tangchai]~/vmware/foo xfs_bmap -vvp test_nosparse | grep -v hole | wc -l

You win.

> My best guess is that your cp test is making the file even more sparse
> by detecting blocks full of zeros and seeking over them, leaving more
> holes.  Not really related to vmware behavior, though.

All right. So next I'll try and downgrade vmplayer.

Just out of couriosity (and stubbornness): Are there any XFS
parameters that might influence fragmentation for the better, in case
I have to put up with a stupid application?

Thanks for your time & thoughts & best regards

Carsten Oberscheid

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