Re: [libvirt-users] Backup a VM (using live external snapshot and blockcommit)

On 09/11/2015 10:18 AM, Jérôme wrote: >> 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. qga with support for quiesce has also been ported to Windows guests. > > 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? If the agent is not running, using --quiesce will fail the entire command; you'd learn pretty quickly to retry without --quiesce for guests that don't know how to handle it. . But if the guest is malicious, it can pretend to be a guest agent, but intentionally refuse to reply to the --quiesce request, and leave libvirt hung waiting for a reply. So it boils down to whether you trust your guests to be reasonable with their guest agent connection (fine if it is your own guests, not so much if you are hosting a cloud for other people's guests). > >>> -> 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-ex... > > I'll have a look at these, thanks.

The libvirt commands were towards the end, in part 3; but the first two parts might give a better understanding of the overall operations of what is happening. >> 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 Yep, sounds like a bug in the wiki, so I fixed it.