On 08/29/2012 09:25 AM, Yehuda Sadeh wrote:
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
We probably wouldn't want to keep it in a single object, since it could
be very large, but it wouldn't be hard to reuse the regular I/O code to
stripe it across objects as well. It wouldn't be very complicated to
implement.
Josh
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