On Tue, Jul 05, 2011 at 01:40:08PM +0100, Stefan Hajnoczi wrote: > On Tue, Jul 5, 2011 at 9:01 AM, Dor Laor <dlaor@xxxxxxxxxx> wrote: > > I tried to re-arrange all of the requirements and use cases using this wiki > > page: http://wiki.qemu.org/Features/LiveBlockMigration > > > > It would be the best to agree upon the most interesting use cases (while we > > make sure we cover future ones) and agree to them. > > The next step is to set the interface for all the various verbs since the > > implementation seems to be converging. > > Live block copy was supposed to support snapshot merge. I think the > current favored approach is to make the source image a backing file to > the destination image and essentially do image streaming. > > Using this mechanism for snapshot merge is tricky. The COW file > already uses the read-only snapshot base image. So now we cannot > trivally copy the COW file contents back into the snapshot base image > using live block copy. It never did. Live copy creates a new image were both snapshot and "current" are copied to. This is similar with image streaming. > It seems like snapshot merge will require dedicated code that reads > the allocated clusters from the COW file and writes them back into the > base image. > > A very inefficient alternative would be to create a third image, the > "merge" image file, which has the COW file as its backing file: > snapshot (base) -> cow -> merge > > All data from snapshot and cow is copied into merge and then snapshot > and cow can be deleted. But this approach is results in full data > copying and uses potentially 3x space if cow is close to the size of > snapshot. Management can set a higher limit on the size of data that is merged, and create a new base once exceeded. This avoids copying excessive amounts of data. > Any other ideas that reuse live block copy for snapshot merge? > > Stefan -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
