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Re: [libvirt] RFC: API additions for enhanced snapshot support



On Tue, Jun 21, 2011 at 2:53 PM, Eric Blake <eblake redhat com> wrote:
> On 06/21/2011 04:30 AM, Daniel P. Berrange wrote:
>>> Upstream qemu is developing a 'live snapshot' feature, which allows the
>>> creation of a snapshot without the current downtime of several seconds
>>> required by the current 'savevm' monitor command, as well as means for
>>> controlling applications (libvirt) to request that qemu pause I/O to a
>>> particular disk, then externally perform a snapshot, then tell qemu to
>>> resume I/O (perhaps on a different file name or fd from the host, but
>>> with no change to the contents seen by the guest).  Eventually, these
>>> changes will make it possible for libvirt to create fast snapshots of
>>> LVM partitions or btrfs files for guest disk images, as well as to
>>
>> Actually, IIUC, the QEMU 'live snapshot' feature is only for special
>> disk formats like qcow2, qed, etc.
>
> Does anyone have pointers to the qemu implementation of monitor commands
> used for live snapshot?

http://repo.or.cz/w/qemu.git/blob/HEAD:/blockdev.c#l572

Jes implemented the snapshot_blkdev command and is integrating guest
agent fsfreeze support.

I think it needs to be a multi-step process instead of just one
command so that libvirt can do storage management for LVM and co.

Stefan


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