RAID Rebuilds....
Not having RAID does not magically protect you from disk failures; you are still going to have significant rebuild workloads as the array tries to re-protect you from a failed disk. And once you factor in protection; that 50PB rapidly becomes 25PB or less; depending how many times you store that data.
Ceph is also not the core storage or even the core object store for OpenStack; something that Fujitsu were corrected on at the press launch. Yes, we do see it commonly implemented with OpenStack but it makes it sound like is part of OpenStack.