Il 25/05/2012 11:43, Stefan Hajnoczi ha scritto: > On Thu, May 24, 2012 at 03:41:29PM +0200, Paolo Bonzini wrote: >> Persistent dirty bitmap >> ======================= >> >> A persistent dirty bitmap can be used by management for two reasons. >> When mirroring is used for continuous replication of storage, to record >> I/O operations that happened while the replication server is not >> connected or unavailable. > > For incremental backups we also need a dirty bitmap API. This allows > backup software to determine which blocks are "dirty" in a snapshot. > The backup software will only copy out the dirty blocks. > > (For external snapshots the "dirty bitmap" is actually the qemu-io -c > map of is_allocated clusters. But for internal snapshots it would be a > diff of image metadata which results in a real bitmap.)
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. Paolo > So it seems like a dirty bitmap API will be required for continuous > replication (so the server can find out what it missed) and for > incremental backup. If there is commonality here we should work > together so the same API can do both. > > Stefan >
