[openstack-dev] [nova] bug 1334398 and libvirt live snapshot support

Daniel P. Berrange berrange at redhat.com
Mon Dec 8 10:28:02 UTC 2014

On Fri, Dec 05, 2014 at 12:50:37PM -0600, Matt Riedemann wrote:
> In Juno we effectively disabled live snapshots with libvirt due to bug
> 1334398 [1] failing the gate about 25% of the time.
> I was going through the Juno release notes today and saw this as a known
> issue, which reminded me of it and was wondering if there is anything being
> done about it?
> As I recall, it *works* but it wasn't working under the stress our
> check/gate system puts on that code path.

Yep, I've tried to reproduce the problem in countless different ways and
never succeeded, even when replicating the gate test VM config & setup
exactly. IOW it is highly load dependant edge case.

IMHO we did a disservice to users by disabling this. Based on my experiance
trying to reproduce it, is something that would work fine for end users 9999
times out of 10000. I think we should just put a temporary hack into Nova
that only disables the code when running under the gate systems, leaving it
enabled for users.

> One thing I'm thinking is, couldn't we make this an experimental config
> option and by default it's disabled but we could run it in the experimental
> queue, or people could use it without having to patch the code to remove the
> artificial minimum version constraint put in the code.
> Something like:
> if CONF.libvirt.live_snapshot_supported:
>    # do your thing

I don't really think we need that. Just enable it permanently, except for
under the gate.

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