Re: [Qemu-devel] [PATCH 0/3] block: block-backup live backup command

[Stefan Hajnoczi]

On Sat, Apr 27, 2013 at 01:37:07PM +0800, Wenchao Xia wrote:
> 于 2013-4-24 0:25, Stefan Hajnoczi 写道:
> > This series adds a new QMP command, block-backup, which takes a 
> > point-in-time
> > snapshot of a block device.  The snapshot is copied out to a target block
> > device.  A simple example is:
> > 
> >    block-backup device=virtio0 format=qcow2 target=backup-20130401.qcow2
> > 
> > The original block-backup blockjob was written by Dietmar Maurer
> > <address@hidden>.  He is currently busy but I feel the feature is worth
> > pushing into QEMU since there has been interest.  This is my version of his
> > patch, plus the QMP command and qemu-iotests test case.
> > 
> > How is this different from block-stream and drive-mirror?
> > ---------------------------------------------------------
> > Both block-stream and drive-mirror do not provide immediate point-in-time
> > snapshots.  Instead they copy data into a new file and then switch to it.  
> > In
> > other words, the point at which the "snapshot" is taken cannot be controlled
> > directly.
> > 
> > block-backup intercepts guest writes and saves data into the target block
> > device before it is overwritten.  The target block device can be a raw image
> > file, backing files are not used to implement this feature.
> > 
>   Besides, compared to snapshot-blkdev, it mainly brings better
> performance by avoid merging later, however, other tool may
> be needed to form an incremental backup, which may be not related to
> this patch.
>   No objection to this patch, but perhaps a better way is using
> internal snapshot by adding base/delta data export support.

Yes, incremental backups would need to be added later.

Stefan