[cinder][nova] fsfreeze hooks issues with cinder snapshot/backup
lyarwood at redhat.com
Wed Sep 1 10:20:21 UTC 2021
On 31-08-21 12:19:54, Sofia Enriquez wrote:
> As far as I can see cinder hasn't implemented this. However, I'm not sure
> about the status of this feature because the last update was on 2014
Oddly enough imageCreate  in Nova does orchestrate this when creating
image based snapshots of volume backed instances  when called directly.
Nova doesn't provide an external API to quiesce an instance so outside
of the imageCreate and os-assisted-volume-snapshots  (only used by
the NFS c-vol backend) flows it isn't going to happen.
> I think it's important to mention that this would only affect the live
> snapshots (handled by Nova) but for any other scenario every cinder driver
> optimized the snapshot/backup creation in a different way.
Well to be clear this specific problem is with Cinder orchestrated live
attached volume snapshots of non-NFS backends.
> This sounds like a good PTG discussion topic. You can add it to the
> planning etherpad here:
I'll add the above to the pad and will try to attend as this will
require work on the Nova side to provide an external API or preferably
an os-server-external-events event to quiesce the instance.
> On Tue, Aug 31, 2021 at 11:52 AM Arthur Outhenin-Chalandre <
> arthur.outhenin-chalandre at cern.ch> wrote:
> > Hello,
> > We are trying to trigger an fsfreeze via a cinder backup or snapshot. We
> > confirmed that the fsfreeze hooks are actually called with a nova
> > snapshot with `/var/log/qga-fsfreeze-hook.log` in the VM, but we can't
> > achieve the same thing with a cinder backup/snapshot attached to the
> > same instance. We are using Wallaby, libvirt, RBD for cinder volumes and
> > RBD as well for cinder-backup.
> > According to this (old) spec , cinder should call the `quiesce()`
> > method in nova during backup/snapshot. We looked in the cinder code and
> > couldn't find any clear evidence that this method is actually called by
> > cinder (but we may have missed something). We added some debug messages
> > on quiesce/can_quiesce/require_quiesce/... in
> > `nova/virt/libvirt/driver.py` and they are never called with a cinder
> > backup/snapshot in our setup while they are (and succeed) if we do a
> > nova snapshot.
> > We are starting to suspect that something is missing in cinder, but it
> > could very well be a problem with our setup as well... Does someone use
> > this feature or know if it should be working/implemented?
> > :
> > https://wiki.openstack.org/wiki/Cinder/QuiescedSnapshotWithQemuGuestAgent#Cinder
> > Cheers,
> > --
> > Arthur Outhenin-Chalandre
> L. Sofía Enriquez
> Software Engineer
> Red Hat PnT <https://www.redhat.com>
> IRC: @enriquetaso
> @RedHat <https://twitter.com/redhat> Red Hat
> <https://www.linkedin.com/company/red-hat> Red Hat
Lee Yarwood A5D1 9385 88CB 7E5F BE64 6618 BCA6 6E33 F672 2D76
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