On Mon, Oct 23, Molle Bestefich wrote: > >This means that every snapshot still has its own exception store. > >This would make deletion of snapshots unnecessary complex. > > Complex, how? > > Necessary operations (in order listed): > * Acquire exclusive lock on this snapshot. > * Check that next snapshot has room for exceptions, abort if not. > * Acquire exclusive lock on next snapshot. > * Move all exceptions to next snapshot. > * Unlock next snapshot. > * Remove this snapshot. > * Done... > > Sounds simple to me, but maybe I'm missing the point. Hmm, sounds simple. Somehow I can't remember exactly where I thought the problem is ... > >We discussed some of the ideas about snapshots here at the dm summit. The > >general ideas are as follows: > > > >- one exception store per origin device that is shared by all snapshots > > Now that sounds complex. But that is something already implemented for clustered snapshots although that is userspace code. > >Although that includes a complete redesign of the exception store code. > > Especially when you say stuff like that :-). > The chained-snapshots approach needs that too. > >The throughput issues should be addressed by only > >writing to one exception store. > > Wouldn't this make debugging more complex, and further add to > the difficulty of snapshot resizing? Resizing? Nope, you only need to resize the exception store thats it. Resizing the chained-snapshots approach is complex however: in the worst case you have to move the exception stores to get enough free space. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
