In [1] the default value for CEPH_LOOPBACK_DISK_SIZE_DEFAULT was changed to be VOLUME_BACKING_FILE_SIZE instead of a fixed value. This will break in some cases as there is no fallback defined for VOLUME_BACKING_FILE_SIZE in devstack/lib/ceph. [1] https://review.openstack.org/403988 Change-Id: I117e36db442c8ef8c469e4149629e8a27d22da22