Re: [Qemu-devel] [question] incremental backup a running vm

[Kashyap Chamarthy <kchamart@redhat.com>]

On Wed, Jan 21, 2015 at 11:39:44AM +0100, Paolo Bonzini wrote:
> 
> 
> On 21/01/2015 11:32, Zhang Haoyu wrote:
> > Hi,
> > 
> > Does drive_mirror support incremental backup a running vm?
> > Or other mechanism does?
> > 
> > incremental backup a running vm requirements:
> > First time backup, all of the allocated data will be mirrored to destination,
> > then a copied bitmap will be saved to a file, then the bitmap file will log dirty for
> > the changed data.
> > Next time backup, only the dirty data will be mirrored to destination.
> > Even the VM shutdown and start after several days,
> > the bitmap will be loaded while starting vm.
> > Any ideas?
> 
> Drive-mirror is for storage migration.  For backup there is another job,
> drive-backup.  drive-backup copies a point-in-time snapshot of one or
> more disks corresponding to when the backup was started.

Zhang, I've been testing the `drive-backup` command via QMP for a little
while, and it works reasonably well. If you'd like to test it you can
quickly try as below, once you have a QEMU instance runing with QMP
(I invoke my QEMU instances with '-qmp tcp:localhost:4444,server').

The below script invokes the 'drive-backup' QMP command (Ensure you're
using the correct disk, your disk ID might be 'drive-virtio-disk1' :-) )
-----------------
#!/bin/bash                                                                                                                                           
set -x
exec 3<>/dev/tcp/localhost/4444
echo -e "{ 'execute': 'qmp_capabilities' }" >&3
read response <&3
echo $response
echo -e "{ 'execute': 'drive-backup', 'arguments':
      { 'device': 'drive-virtio-disk0', 'sync': 'full', 'target':
      '/export/backup-of-vm1.qcow2', 'mode': 'absolute-paths', 'format': 'qcow2' } }" >&3
read response <&3
echo $response
-----------------

Once the above is invoked succesfully, you can see the success of the
command on the shell where your QMP server is running:
-----------------
[. . .]
char device redirected to /dev/pts/8 (label charserial0)
QEMU waiting for connection on: disconnected:tcp:localhost:4444,server
Formatting '/export/backup-of-vm1.qcow2', fmt=qcow2 size=53687091200 encryption=off cluster_size=65536 lazy_refcounts=off
-----------------

> 
> Incremental backup is being worked on.  You can see patches on the list.
> 
> Paolo
> 

-- 
/kashyap