Re: [Xen-users] Converting AND shrinking domU

[James Pifer <jep@xxxxxxxxxxxxxxxx>]

On Thu, 2010-04-22 at 14:25 -0600, Nick Couchman wrote:
> > 
> > 
> > ïOCFS2 does not allow sparse disks? I've never heard of that. I have
> had
> > tickets open with novell and they have never said it's not
> supported.
> > I've emailed this list saying we're using ocfs2 and sparse files and
> > nobody has raised any flags before (which could be understandable
> being
> > a mailing list).
> 
> Perhaps OCFS2 on SLES11 does support sparse files.  On SLES10, OCFS2
> definitely does not support sparse files - if you try to create a sparse
> disk file, either via virt-manager or using a command like "dd
> if=/dev/zero of=disk0 bs=1G seek=10", it actually takes up 10 GB of
> space on the filesystem and disk, not the 10MB or so that you would
> expect from a sparse disk file.

That has not been my experience. I started with sles10 using ocfs2 with
sparse files, and they were/are definitely sparse. I still have a couple
of the sles10 boxes running. I started with a 300 gb ocfs2 clustered
between a couple xen servers and had a couple dozen domUs. I had to add
a second 300 gb ocfs2 volume as my domUs approached 30. My linux domUs
were logically 50gb. My total logical disk space being used on those two
300 gb volumes was 1.3 tb. ïI would use the du -B1 -s commands to
verify.

I only know all of this because of all the tracking/moving/recovering I
had to do when problems started. I also started tracking sizes in
planning to go away from ocfs2 and away from spares files. 

Either way, since I've moved most of my domUs off of ocfs2 my
environment has been much more stable, so I'm almost definitely getting
away from ocfs2 and sparse files. 

Thanks for the thin provisioning explanation on the SAN. I don't believe
our SAN supports it. 

Thanks,
James


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