NAS-Oriented Hard Drives, With A Twist
When power users and small offices populate their network-attached storage devices with hard drives, they typically lean on desktop-oriented disks in protective RAID arrays, if only because they're less expensive. Really, though, those drives are well-suited for life in a NAS, with other mechanical devices clacking around. For example, Seagate’s Barracuda hard drives aren’t certified for the continuous operation networked-storage imposes. There are a handful of exceptions, of course, like Hitachi's Deskstar, which the company says can handle the demands of 24x7 availability. But, at the end of the day, they're still desktop disks intended for client workloads.
Nearline Hard Drives
In order to achieve more robust reliability in a multi-drive array, you really need to look at purpose-built nearline hard drives. They're optimized, both at the firmware and hardware levels, to serve up higher endurance and reliability.
The usual criteria for evaluating hard drives, such as speed and price per gigabyte, are still important in the design of nearline storage. But there are other added considerations taken into account as well like reliability, a low thermal profile, and moderate power consumption. The mechanical components of nearline drives are improved to be more robust than their desktop counterparts as they cope with the increased heat of continuous operation. Manufacturers build the drives to higher, more stringent, standards, and step up their testing and quality control.
Those enhancements aren't free, of course. Nearline disks are more expensive than comparable desktop drives. They do tend to come with a longer warranty, though.
Enterprise and nearline drives like Hitachi's Ultrastar, Seagate's Constellation, and Western Digital's RE4 families feature up to five platters and spin at 7200 RPM more. In order to operate in an environment with many other mechanical storage devices, they sport rotational vibration (RV) sensors that allow them to optimize head position to avoid longer seek times due to vibrations from other drives. Typically, desktop drives are rated for 2400 power-on-hours per year, with Seagate's Barracuda 7200.14 standing in as our example. Nearline drives, on the other hand, are good for up to 8760 hours per year, the 24x7 availability equivalent.
A NAS-Oriented Alternative To Nearline: Western Digital Red
Western Digital's Red family is positioned in between the desktop and nearline drives. They're meant neither for typical desktop usage nor for large 19-inch rack-mounted servers. Instead, they’re being aimed at home office and small office network-attached storage appliances.
The resulting piece of hardware includes a blend of features from desktop and nearline drives. For instance, the 5400 RPM spindle speed is typical of entry-level desktop drives, while 24x7 operation is taken from the nearline playbook. The Western Digital Red is available in capacities of 1, 2, and 3 TB. The two larger-capacity models include SATA 6Gb/s connectivity, and they're the offerings we have in the lab today.