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

MORITA Kazutaka morita.kazutaka at lab.ntt.co.jp
Sun Jan 10 16:02:12 CET 2010

On Sun, Jan 10, 2010 at 7:16 PM, Chris Webb <chris at arachsys.com> wrote:
> 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;

Yes. It is same as zvol of ZFS and Amazon EBS.

>  - 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?

Yes, sheepdog is expected to be so.

> 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?

Thanks for the valuable advice!
Such a operation is not supported yet.

Implementing the following operations looks to be useful, yes?

- make a patch
 $ shepherd diff src_vdi:src_tag dst_vdi:dst_tag > delta_file

- apply a patch
 $ shepherd apply vdi:tag delta_file


Kazutaka Morita

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