Its a lower priced thunderbolt external drive unit that holds 4 2.5" drives. The Drobo mini is probably its main competitor. From the reviews I've read, it appears to use OSX' RAID feature and not any hardware raid since you need to set it up in the Disk Utility App. Is that true, or am I misunderstanding things? How's the performance of the J4 via thunderbolt? At 369 and up, its a bit pricey, what external Thunderbolt drives would be better (and faster) but not terribly more expensive?