I've done as you suggested, and configured Nova to use CEPH as it's backend. It worked in a way - now dashboard says that each of my two compute nodes has 3.6TB of storage. I see how this can introduce some issues in the future, as this number, obviously, taken from CEPH. I have 4 OSDs, 1TB each, plus some overhead, results in CEPH stating it has 3724GB of storage. I guess this is the number Nova gets from CEPH monitors as it's available storage. But I also have pool size of 2, which means every 1GB of data takes 2GB+overhead of storage in CEPH, and Nova is not aware of that. Of course, situation is eased a little bit by the fact that CEPH thin-provisions block devices, so 100GB disk only takes as much storage as there's really needed. But anyway, this can possibly lead to a situation where there's no storage left in CEPH, but Nova doesn't know this. So I'm not sure this is the end solution.