[libvirt] [RFC]: Snapshot API
Chris Lalancette
clalance at redhat.com
Wed Mar 24 14:57:55 UTC 2010
On 03/24/2010 10:40 AM, Paolo Bonzini wrote:
>> > If you do not want to allow setting the parent, you can also add a
>> flag
>> > --inactive to virsh snapshot-create that would create the snapshot
>> > without making it active. Then you would make<parent> an
>> informational
>> > field about which snapshot was*active* when the new one was created.
>>
>> That's more or less what the<parent> field is supposed to mean, although
>> I'm not sure I understand your proposal about --inactive. How would you
>> go about doing that?
>
> Say you were on snapshot A and the guest has a problem. The easiest fix
> is reverting to snapshot A, but you want to investigate it anyway. You
> create snapshot B with --inactive and, if you want, you can move the
> snapshot to another machine to activate it and look at it more calmly.
>
> If the problem reproduces, you can create another inactive snapshot, and
> so on.
>
> Alternatively, say the easiest fix is stopping and starting a daemon,
> but again you want to keep a snapshot to investigate it anyway. You can
> create the inactive snapshot B and stop/start the daemon _while the
> system is live and running under snapshot A_, i.e. without manually
> shutting down and rebooting.
>
> Is this clearer?
Much clearer, thank you. So you are still snapshotting the *current*
image, but sort of storing it away for future reference. That's where
my confusion was.
This seems like a good debugging aid; the only question is whether the
hypervisors can support this kind of thing. I guess we can always emulate
it by taking a snapshot and then immediately reverting to the parent.
--
Chris Lalancette
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