Comment 2 for bug 1578036

Thanks for the great debugging.

I've confirmed that this issue still exists in master and is present even with a single ceph cluster. Hence I've changed the bug title a bit.

Working hypothesis is that since the ceph backup driver code has not changed, this issue was introduced by the work done in mitaka to decouple backup and volume services. That work relies on using brick connector and rpc to the volume service to get the volume that is to be backed up and likely something in that chain is losing the 'rbd_image' attribute of the volume file so that the ceph backup driver treats ceph volumes as if they were from foreign backends and does a full backup every time.

I'll instrument the code and see if we can figure out a fix.