On Wed, Aug 29, 2012 at 9:15 AM, Josh Durgin <josh.durgin@xxxxxxxxxxx> wrote:
> On 08/29/2012 06:40 AM, Alexandre DERUMIER wrote:
>>
>> Hi,
>>
>> I'm trying to take a full vm state snapshot with savevm monitor command
>> (qemu 0.12rc1 + rbd 0.48.1)
>>
>> it seem that vmstate is not saved in the snapshot. (I also don't notice
>> any vm hang during snapshot)
>> Snapshot of disk is correctly made.
>
>
> AFAIK the only block backend that supports saving the vmstate is qcow2.
> For rbd, the savevm/loadvm monitor commands are equivalent to
> 'rbd snap create' and 'rbd snap rollback'. They just save/rollback the
> disk.
>
>
>> using loadvm monitor command, rollback correctly to disk snapshot but vm
>> hang.
>
>
> If you don't quiesce i/o i.e. via xfsfreeze (it works on the vfs level
> now, so it's not xfs-specific anymore) before snapshotting a running
> vm, the fs might require a fsck to be usable. This is only rolling back
> the disk, and not the memory state, so doing it while the vm is running
> is likely to cause problems.
>
>
>> starting qemu with -loadvm snapshotname give
>> kvm: Error -22 while loading VM state
>>
>>
>> Is it normal ? Not implemented ?
>
>
> bdrv_{save|load}_vmstate are not implemented.
>
How complicated would it be to implement it? Looking at the api it
seems trivial. We can add a new block with a .vmstate prefix and keeps
the raw data on it. We should probably add some librbd functionality
that stores and retrieves alternative data payloads and use it for
that.
Yehuda
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