The rbd diff-related commands compare points in time of a single
image. Since children are identical to their parent when they're cloned,
if I created a snapshot right after it was cloned, I could export
the diff between the used child and the parent. Something like:
rbd clone child parent@snap
rbd snap create child@base
<use child image>
rbd snap create child@changed
rbd export-diff child@changed --from-snap base child_changes.diff
the questions are:
1. Does the child@base really necessary? It seems point the same obj with
parent@snap, why should'n I use the parent@snap instead?
2. If I create child@base, comparing with use child image directly, are there
some performance redundant or storage increment when writing the child image
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