Am 07.09.2010 22:41, schrieb Anthony Liguori: > There's two types of snapshots that I think can cause confusion. > There's CPU/device state snapshots and then there's a block device snapshot. > > qcow2 and qed both support block device snapshots. qed only supports > external snapshots (via backing_file) whereas qcow2 supports external > and internal snapshots. The internal snapshots are the source of an > incredible amount of complexity in the format. > > qcow2 can also store CPU/device state snapshots and correlate them to > block device snapshots (within a single block device). It only supports > doing non-live CPU/device state snapshots.
Which is not a property of the format, but of the implementation. I think it shouldn't be too hard to introduce live snapshots. > OTOH, qemu can support live snapshotting via live migration. Today, it > can be used to snapshot CPU/device state to a file on the filesystem > with minimum downtime. > > Combined with an external block snapshot and correlating data, this > could be used to implement a single "snapshot" command that would behave > like savevm but would not pause a guest's execution. We'd need fields for referencing a VM state file from a QED image, just like it's already done for backing files. Kevin
