In keeping with Raptor tradition, WD’s VelociRaptor breaks new performance ground for SATA drives by combining a 3GB/s SATA interface with a 10K-RPM rotational speed. That makes it a nice option for servers, among other things, and WD decided to enhance that proposition by making the VelociRaptor a 2.5″ drive. The drive then adapts to 3.5″ drive bays by snapping into a combination drive sled/heat sink/paper weight, if needed.
Trouble is, the power and SATA I/O connectors remain on the back of the 2.5″ drive (scroll to the bottom here for a look), completely out of place for a 3.5″ hot-swap enclosure to a SAS/SATA backplane. Tragicomic, one would have to say. (link)