2.5" hard drives are most commonly associated with notebooks. However, they've also become a staple of server installations looking to cram as much storage as possible into rackmount chassis. Today, Seagate makes that job a little easier with the Constellation.2, which the company says is the first enterprise-class 2.5" model to offer a terabyte of storage capacity.
The Constellation gets to the terabyte mark by stacking four 250GB platters. 2.5" hard drives are typically limited to two platters with the common 9.5-mm drive thickness used for notebooks and three platters for the 12.5-mm spec typical of external hard drives. To accommodate the Constellation's four-story stack, Seagate uses a drive casing that measures 15 mm in thickness.
Since this is a "capacity-optimized drive," Seagate hasn't cranked up the spindle speed. The Constellation's platters rotate at 7,200 RPM, just like the latest crop of notebook models. Those drives are limited to 3Gbps Serial ATA interfaces, but Seagate has a couple of more exotic options for the Constellation: 6Gbps SATA and 6Gbps SAS. The faster interfaces aren't strictly necessary given the drive's 115MB/s maximum sustained data rate, but they could speed up burst transfers from the 64MB DRAM cache.
If you opt for a SAS interface, the Constellation.2 is available in 1TB or 500GB capacities. Going the SATA route adds a 250GB option, which Seagate expects to be used as a boot drive in blade servers. All versions have built-in encryption capabilities and five years of warranty coverage. Based on the purportedly excellent reliability of the first-gen Constellation.1, which had a Mean Time Between Failure rating of 1.2 million hours, Seagate has bumped the .2's MTBF up to 1.4 million hours.
Power consumption is rather important for a drive that's said to enable rack-mount storage densities of 76TB per square foot. According to Seagate, a terabyte Constellation.2 with a SAS interface draws 3.85W at idle and 6.4W under load. A PowerChoice feature is also available that's claimed to cut idle power consumption down to as little as 1.87W, a reduction of over 50%. Power draw can be reduced further by going with a SATA interface, which shaves about half a watt off the total.