RBDs support having snapshots taken of them. Snapshots are a read-only copy of the RBD image that persists its state from the point in time in which it was taken. Multiple snapshots can be taken to retain the RBDs history through time, if desired. The process of taking a snapshot of an RBD is extremely quick, and there is no performance penalty for reads going to the source RBD. However, when a write hits the source RBD for the first time, the existing contents of the object will be cloned for us by the snapshot, further I/O will have no further impact. This process is called copy-on-write and is a standard way of performing snapshots in storage products. It should be noted that this process is greatly accelerated in ...
Snapshots and clones
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