[fedora-virt] Suspending VMs on host shutdown

Eric Blake eblake at redhat.com
Mon Aug 15 13:46:57 UTC 2011


On 08/15/2011 07:38 AM, Dor Laor wrote:
> On 08/15/2011 05:38 AM, Eric Blake wrote:
>> On 08/15/2011 04:12 AM, Tom Hughes wrote:
>>> My specific example was that this morning qemu-kvm updated from
>>> 0.15.0-1.fc15 to 0.15.0-0.3.201108040af4922.fc15 and shortly after that
>>> I restarted my host only to find that the VM that had been running for
>>> some time wouldn't start. Looking at the logs showed:
>>>
>>> Unknown savevm section or instance 'kvmclock' 0
>>> load of migration failed
>>
>> That's not good, and it would be nice if we could improve the situation.
>> However,
>
> The above is a bug, there is a mechanism to take care of preserving
> older version format by specifying a 'machine type' flag using -M
> qemu0.15. I do think it is there on default so it is just a but in this
> case.
>
> In general, I doubt that savevm is a good thing on host shutdown anyway.

Libvirt isn't using savevm on host shutdown, rather it is using 'migrate 
to file'.  As long as qemu is upgraded (not downgraded), and newer qemu 
can do migration from older file, then things are okay.  The problem 
here is when newer qemu refuses to migrate from older file; you would 
have the same problem using migration between two machines, one running 
older qemu and the other running a newer one.

> When the guests will be restored, they'll have a time gap and also their
> tcp connections will probably stop be relevant. It's better to trigger
> internal guest hibernation (which has some caveats now) or shutdown the
> guest as you've said).

And how does one go about triggering internal guest hibernation from the 
host libvirt?

-- 
Eric Blake   eblake at redhat.com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org


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