- When RBD is used for ephemeral disks and image storage, make
snapshot use Ceph directly, and update Glance with the new location.
In case of failure, it will gracefully fallback to the "generic"
snapshot method. This requires changing the typical permissions
for the Nova Ceph user (if using authx) to allow writing to
the pool where vm images are stored, and it also requires
configuring Glance to provide a v2 endpoint with direct_url
support enabled (there are security implications to doing this).
See http://docs.ceph.com/docs/master/rbd/rbd-openstack/ for more
information on configuring OpenStack with RBD.