Comment 10 for bug 1251590

Having the correct size on an ephemeral backing file is important IMHO only on new instance spawning, since it may expects a filesystem with the size promised by the flavor. During migration it's going to be rebased anyway with the existing information from the qcow2 layer.

So to understand the second issue a bit more, are we going to have a backing file of some name ephemeral_SIZE_OS_TYPE but not of size SIZE?