The Rack-Moutnable ProLiant Storage System/U, Model 2, is a dual bus, external hot-pluggable 4U rack-mountable storage system with capacity for up to eight 1.6" high hot-pluggable disk drives or twelve 1" high hot-pluggable disk drives, supporting Wide-Ultra SCSI-3 transfer rates (outside the server) with 40MB/s per SCSI channel.