RAID5 is just about useless with disk above 2TB, as you're pretty much guaranteed a failure during a rebuild with desktop grade drives. RAID6 is fine though (I use it on my fuck the MPAA array with 2TB disk.) I REALLY hate software and hardware raid for disk >2TB, it just is piss poor. File systems built for large volumes like ZFS do a much better job. I'm assuming drobo doesn't use that, but I guess I could be wrong.