Strange fragmentation in nearly empty filesystem

[Carsten Oberscheid]

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?

Yep.

>  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 at tangchai]~/vmware/foo cp --sparse=never foo.vmem test_nosparse

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

[co at tangchai]~/vmware/foo xfs_bmap -vvp test_nosparse | grep hole | wc -l
0

[co at tangchai]~/vmware/foo xfs_bmap -vvp test_nosparse | grep -v hole | wc -l
9


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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