Hi Eric. Thank you so much for your quick and relieving answer. Le 2015-09-11 17:05, Eric Blake a écrit :
Yes, using active block-commit is the ideal way to perform a live backup.
Great.
Yep, that about covers it. Note that the --quiesce step in snapshot creation requires qemu-guest-agent running in the guest, and that you trust interaction with your guest.
Yes, I think I get this. I don't really figure out what these cases could be. We're using Debian Jessie and I installed qemu-guest-agent. Other VM could use other systems, but most likely Linux based. Do you mean that, in cases where you shouldn't trust the guest, using '--quiesce' might end up being worse than nothing? Or just useless?
-> Anything wrong about my snapshot-create-as and blockcommit command lines? May I remove the snapshot with only a rm command?
Looks correct to me, and matches my recent KVM Forum slides: http://events.linuxfoundation.org/sites/events/files/slides/2015-qcow2-expan...
I'll have a look at these, thanks.
Now, a few side questions, as I might have messed up with the VM I was experimenting with.
I used the same command lines as described above, except I didn't pass the '--no-metadata' option. Once the backing file was copied, I deleted the snapshot qcow2 file and thought I was done with it, until I realized the snapshot was still listed by virsh snapshot-list. And I couldn't find a way to delete it. (For the record, I asked on serverfault about that [3].)
virsh snapshot-delete --metadata $dom $badname
to remove $badname snapshot that no longer exists because you changed things behind the scenes.
Before removing the .xml file, I tried the command indicated in the wiki [1] with no success. "NOTE-2: Optionally, you can also supply '--no-metadata' option to tell libvirt to not track the snapshot metadata -- this is useful currently as at a later point when you merge snapshot files, then you have to explicitly clean the libvirt metadata (by invoking: virsh snapshot-delete vm1 --delete --current -- repeat this as needed.)" Shouldn't the virsh snapshot-delete vm1 --delete --current be rephrased as virsh snapshot-delete vm1 --metadata --current ? I see '--delete' is not listed in the man. Or even virsh snapshot-delete vm1 --metadata $badname since after the blockcommit, the snapshot is unused, I'm not sure it is considered current. Anyway, I'm glad you confirm I now have the correct sequence. Thanks again. Enjoy the WE. [1] http://wiki.libvirt.org/page/Live-disk-backup-with-active-blockcommit -- Jérôme