efficient snapshot rollback
Rolling back images is painfully slow. Yes, I know, "rbd clone", but this creates another image and automatic-snapshotting-backuppers get failed. Why not to bring image to the state of specified snapshot ?
Only possible if you are rolling back to the most recent snapshot. If you are rolling back to an older snapshot, you would need to copy the older data to the HEAD revision instead of just deleting the HEAD revision to expose the most recent snapshot.
Yes, ability to do FAST rollback to latest snapshot will be huge improvement, IMHO.
I quickly hacked this up and it turns out the OSDs don't actually allow you to do this. The low-level, internal transactions within the OSD will still clone the HEAD object and then "delete" it, which results in a zeroed object at HEAD. There is nothing RBD can do -- you can perhaps open a new ticket against RADOS to optimize snap rollback directly.
So, I have done that.