[Users] re-thin a disk
Richard W.M. Jones
rjones at redhat.com
Fri Mar 15 17:23:24 UTC 2013
On Wed, Mar 13, 2013 at 09:23:04PM +0000, Jonathan Horne wrote:
> I have a virtual machine with a 500GB thin-provisioned disk, and on
> it is about 2GB of data. Due to a pvmove operation I am running,
> the 500GB disk with 2GB of data is growing and growing and is
> currently 180GB in size, and im sure it will go all the way to the
> 500GB before it stops.
>
> When this process is finished, is there a way to re-thin the disk
> back down to the proper size again? What about the export/import
> process? Would that export it to the data size, not the block size?
There's not a way to do this in-place currently, although we're
working on it.
If you can accept a copy, then 'qemu-img convert' will automatically
sparsify disks, although it only works if there is no left-over data
in the blocks.
Also requiring a copy, virt-sparsify can fully sparsify a disk even if
it has left-over but unused data blocks.
See also:
http://libguestfs.org/virt-sparsify.1.html
http://libguestfs.org/guestfs-faq.1.html#why-doesnt-virt-sparsify-work-on-the-disk-image-in-place-
- - -
Your question also made me wonder if there was a tool to do an
in-place sparsification of a thin provisioned DM device, but there
doesn't seem to be anything for that. *If* such a tool did exist,
then you could use it in conjunction with the following guestfish
command:
http://libguestfs.org/guestfish.1.html#zero-free-space
ie. something like:
guestfish -a /dev/vg/guest
><fs> run
><fs> list-filesystems
# for each filesystem do:
><fs> mount /dev/XXX /
><fs> zero-free-space /
><fs> umount /
followed by running the non-existent thinning tool.
Rich.
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
virt-p2v converts physical machines to virtual machines. Boot with a
live CD or over the network (PXE) and turn machines into KVM guests.
http://libguestfs.org/virt-v2v
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