On Sat, Apr 27, 2013 at 01:37:07PM +0800, Wenchao Xia wrote: > δΊ 2013-4-24 0:25, Stefan Hajnoczi ει: > > 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 > > <diet...@proxmox.com>. 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
