The WD My Book VelociRaptor Duo is an external hard drive that contains two 1TB 10,000rpm hard drives that can be configured in RAID 0, RAID 1, or JBOD modes. It connects via Thunderbolt and provides transfer speeds up to 400MB/s when used with Mac or Windows computers. The compact design allows two drives to be daisy chained together via Thunderbolt for additional storage capacity.