> > Your use of "current-state" is confusing me because AFAICT, > > current-state is just semantically another snapshot. > > > > It's writable because it has no children. You only keep around one > > writable snapshot and to make another snapshot writable, you have to > > discard the former. > > > > This is not the semantics of qcow2. Every time you create a snapshot,
> > it's essentially a new image. You can write directly to it. > > > > While we don't do this today and I don't think we ever should, it's > > entirely possible to have two disks served simultaneously out of the > > same qcow2 file using snapshots. > > No, CQ is describing the semantics of internal snapshots in qcow2 > correctly. You have all the snapshots that are stored in the snapshot > table (all read-only) plus one current state described by the image > header (read-write). That's also the semantics of VMware's external snapshot. So there is no difference in semantics. It is just a difference in implementation and performance. Regards, ChunQiang (CQ) Tang Homepage: http://www.research.ibm.com/people/c/ctang
