Its RAID6, over 3 trays of disks. Each tray is a RAID group, with its own hot spare.
Its a SAN (albeit with only 2 servers and no switch in this case) all the clever stuff happens before the server goes near it.
Those "disks" are just LUN's presented to the server and are not physical disks at all.
I've got some pics of the hardware somewhere, i'll try and host them.