Hi, We know snapshot is on a point of time. Is this point of time tracked internally by some sort of sequence number, or the timestamp showed by "snap ls", or something else? I noticed that when "deep cp", the timestamps of all snapshot are changed to copy-time. Say I create a snapshot at 1PM and make a copy at 3PM, the timestamp of snapshot in the copy is 3PM. If I rollback the copy to this snapshot, I'd assume it will actually bring me back to the state of 1PM. Is that correct? If the above is true, I won't be able to rely on timestamp to track snapshots. Say I create a snapshot every hour and make a backup by copy at the end of the day. Then the original image is damaged and backup is used to restore the work. On this backup image, how do I know which snapshot was on 1PM, which was on 2PM, etc.? Any advices to track snapshots properly in such case? I can definitely build something else to help on this, but I'd like to know how much Ceph can support it. Thanks! Tony