LVM thin provisioning and virt-manager

[Chris Murphy]

On Oct 15, 2013, at 4:30 PM, Josh Stone <jistone at redhat.com> wrote:

> On 10/15/2013 02:46 PM, Richard W.M. Jones wrote:
>> On Tue, Oct 15, 2013 at 03:29:38PM -0600, Chris Murphy wrote:
>>> The better snapshots sound ideal for VM testing. Snapshot a
>>> successful install and then try to break the snapshot. Etc.
>>> 
>>> Presently virt-manager ignores thinp pools and only creates
>>> conventional LV's. I haven't tried using virsh to force it to use an
>>> already created virtualsize LV as backing, but I'm wondering if it
>>> should work. If not, is there a rough time frame on such support?
> 
> FWIW, I have tried, and my VMs with thin LV storage are working fine,
> even though the libvirt storage pool barfs on the VG.  (bz924672)

So you're using virsh to compel it to use the LV I take it?

> 
>> Is using LVs for this over-thinking things?
> 
> One nice aspect with thin LVM snapshots is you don't need to worry about
> preserving the chain of origin.  There's no backing file except the main
> thinpool itself.  One can snapshot to arbitrary depths, and delete old
> images anywhere, freeing the unique blocks but keeping whatever is still
> shared.

Yes, this is like btrfs snapshots. It doesn't matter whether the original or snapshot subvolume is destroyed, whichever subvolume remains is equally usable.

Chris Murphy