[one-users] OpenNebula and ceph: why "rbd copy" rather than "rbd clone"?

Stuart Longland stuartl at vrt.com.au
Thu Feb 20 22:16:03 PST 2014

Hi all,

Silly question.  I've just thrown together an OpenNebula cluster for
evaluation purposes and have it using a back-end Ceph cluster for storage.

Image creation works, but one thing I observe is that the VMs sit in the
PROLOG stage for a long time.  During this process, I see an rbd process
busily copying the image to a temporary rbd for the instance.

The call specifically is a 'rbd copy' command.  I see in the manual
pages for rbd:

>        clone [parent-snapname] [image-name]
>               Will create a clone (copy-on-write child) of the parent snapshot.  Object order will be  identical  to
>               that of the parent image unless specified. Size will be the same as the parent snapshot.

Surely this would be more efficient than creating copies of the images.
 Is there a reason why 'copy' was chosen rather than 'clone' in OpenNebula?
Stuart Longland
Systems Engineer
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