Re: [Qemu-devel] Block job commands in QEMU 1.2 [v2, including support for replication]

[Paolo Bonzini <pbonzini@redhat.com>]

Il 25/05/2012 14:09, Stefan Hajnoczi ha scritto:
>> > 
>> > Perhaps that be simply a new qemu-img subcommand?  It should be possible
>> > to run it while the VM is offline.  Then the file that is produced could
>> > be fed to blockdev-dirty-enable.
> For both continuous replication and incremental backups we cannot
> require that the guest is shut down in order to collect the dirty
> bitmap, I think.

Yes, that is a problem for internal snapshots.  For external snapshots,
see the drive-mirror command's sync parameter.  Perhaps we can add a
blockdev-dirty-fill command that adds allocated sectors up to a given
base to the dirty bitmap.

> I think we really need a libvirt API because a local file not only has
> permissions issues but also is not network transparent.  The continuous
> replication server runs on another machine, how will it access the dirty
> bitmap file?

This is still using a "push" model where the dirty data is sent from
QEMU to the replication server, so the dirty bitmap is not needed on the
machine that runs the replication server---only on the machine that runs
the VM (to preserve the bitmap across VM shutdowns including power
loss).  It has to be stored on shared storage if you plan to run the VM
from multiple hosts.

Paolo