[cinder][nova] fsfreeze hooks issues with cinder snapshot/backup

Jay Bryant jungleboyj at gmail.com
Wed Sep 1 13:34:49 UTC 2021

On 8/31/2021 10:19 AM, Sofia Enriquez wrote:
> Hello,
> 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[1]
I remember being a part of these discussions and the fact that there was 
interest in getting it working.  I am wondering if this was just a case 
where no one followed through on implementation. It might be that we 
encountered an unexpected challenge that I don't remember.

Either way, I do agree that this would be a good topic for the PTG.

> 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.
> This sounds like a good PTG discussion topic.  You can add it to the 
> planning etherpad here:
> https://etherpad.opendev.org/p/yoga-ptg-cinder-planning 
> <https://etherpad.opendev.org/p/yoga-ptg-cinder-planning>
> There's also info about the dates and times we'll be meeting on that 
> etherpad.
> Cheers,
> Sofia
> [1] 
> https://blueprints.launchpad.net/cinder/+spec/quiesced-snapshots-with-qemu-guest-agent 
> <https://blueprints.launchpad.net/cinder/+spec/quiesced-snapshots-with-qemu-guest-agent>
> On Tue, Aug 31, 2021 at 11:52 AM Arthur Outhenin-Chalandre 
> <arthur.outhenin-chalandre at cern.ch 
> <mailto: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 [0], 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?
>     [0]:
>     https://wiki.openstack.org/wiki/Cinder/QuiescedSnapshotWithQemuGuestAgent#Cinder
>     <https://wiki.openstack.org/wiki/Cinder/QuiescedSnapshotWithQemuGuestAgent#Cinder>
>     Cheers,
>     -- 
>     Arthur Outhenin-Chalandre
> -- 
> L. Sofía Enriquez
> she/her
> 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 
> <https://www.facebook.com/RedHatInc>
> <https://www.redhat.com>
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