Seagate is reportedly working on a 6 terabyte hard drive, which it plans to roll out in Q2 (April-June), 2014. According to leaked company road-maps, the drive could be launched in the later part of the quarter, and could be branded in the new Constellation ES.3 Megalodon series. The drive will be built in the 3.5-inch form-factor, its interface, however, remains unclear (whether it's SATA or SAS).
The drive tucks in six 1000 GB platters. Competitor HGST's 6 TB Helium drive, in comparison, runs seven 857 GB ones. Given its enterprise credentials, Seagate could give it at least 7,200 RPM spindle speeds.