[Sheepdog] [PATCH 0/5] modify the usage of snapshot and cloning

[Chris Webb]

MORITA Kazutaka <morita.kazutaka at lab.ntt.co.jp> writes:

> - create a clone image (only from a sheepdog image)

Hi. Can I clarify the semantics of this operation? Am I right that
 
  - you can clone a new image from a snapshot of an existing image, but not
    directly from an existing image;

  - one you've cloned a new image, you will be able to delete the source
    snapshot and the whole original image without losing the clone, going
    from two references counts to the shared blocks to just one again?

(I can't test the latter behaviour yet because image delete isn't
implemented, but I'm guessing based on the description of 'clone' and the
syntax you've suggested.)

With my "infrastructure provider's" hat on, the other piece of information
which exists inside sheepdog and would be nice to expose is a way to know
which blocks differ between two snapshots of the same image. This could then
be used to efficiently implement offsite backup to another sheepdog cluster,
just sending the block-diffs from the previous backup. Perhaps another
operation to include in the client library?

Best wishes,

Chris.