The 4.8TB VTrak J-Class Expansion Chassis from Apple is an expansion hard drive unit for the Promise VTrak E-Class RAID subsystem. It is populated with 16 300GB SAS 15,000rpm hard disks. The chassis is in a 3U rackmount form factor and requires the Promise VTrak E-Class RAID to function. This expansion chassis offers all of the same benefits as its host, making it an excellent option for VTrak E-Class owners who require extra storage capacity.