libvirt unable to create more than one snapshot

[Thomas Stinner]

I try to create an external snapshot of a running VM to be able to backup the machine.

I do the following:

virsh snapshot-create-as --domain Windows10Pro Snapshot3 --diskspec hda,file=/data/snapshots/Windows10ProSnapshot3 --disk-only --atomic --quiesce --no-metadata

After backing up the data i blockcommit the snapshot:

virsh blockcommit Windows10Pro hda --active --verbose --pivot

I then manually delete the Snapshot from the disk.

This works perfectly for the first time.

The second time i want to do it, i get the following error:

error: internal error: unable to execute QEMU command 'transaction': The feature 'snapshot' is not enabled

I can only solve this by rebooting the machine. Restarting libvirtd-bin or qemu-kvm does not help.

This is Ubunut 16.04, libvirt is 1.2.21-2ubuntu7

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Dominique Ramaekers (dominique-ramaekers)]

I confirm.

I use this procedure to backup my VM’s: http://wiki.libvirt.org/page/Live-disk-backup-with-active-blockcommit

It works on my current production host:
Compiled against library: libvirt 1.2.16
Using library: libvirt 1.2.16
Gebruikte API: QEMU 1.2.16
Draaiende hypervisor: QEMU 2.1.0

Now I’m doing a test on a testing host:
Compiled against library: libvirt 1.2.21
Using library: libvirt 1.2.21
Gebruikte API: QEMU 1.2.21
Draaiende hypervisor: QEMU 2.5.0

My testing host is identical to my production but now release-upgraded tot Xenial.

On my testing host I get this error when I want to create for the second time an external snapshot :
fout: internal error: kan QEMU commando 'transaction' niet uitvoeren: The feature 'snapshot' is not enabled

After shutting down the guest and starting up the guest, I can do one cycle of external snapshotting + active block commit.

[Dominique Ramaekers (dominique-ramaekers)]

This is actualy a qemu bug. Not a libvirt bug.

It seems, a fix is released on Red Hat: https://bugzilla.redhat.com/show_bug.cgi?id=1300209

Could this fixed be processed please? Otherwise, in Xenial we don't have a decent way to backup our machines.

Thanks in advance.

[Serge Hallyn (serge-hallyn)]

Thanks, @Dadio, I'll cherrypick the patch unless #qemu points to objections.

[Serge Hallyn (serge-hallyn)]

It should be fixed in qemu 1:2.5+dfsg-5ubuntu5