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Surveillance drives are worth watching

Simon Sharwood

Seagate has released a new generation of its hard drives for surveillance systems.

The drives are standard 3.5 inch SATA affairs and ship in 250GB, 500GB and 750GB variants. A 1TB monster is around the corner.

Nothing out of the ordinary there.

But inside, these machines are rather different, as Kevin Lee, Seagate's Managing Director of Channel Sales and Marketing in Asia Pacific explains.

"A PC or server writes to its drive occasionally," he says. "But a video surveillance device writes to its drives 24x7."

Conventional drives also have the luxury of a few microseconds in which to verify that the data they just wrote made it safely onto the platter as either a 1 or a 0. Surveillance drives have no such luxury because, as Lee says, "even a delay of a second or two could mean you miss a murder."

Surveillance drives are supposed to see everything, making the pause to verify data a deleterious delay. The machines compensate by using some of the less-used bits of the ATA-7 instruction set to instruct the drive that it simply cannot pause for anything because video is being written to the device.

Various components of the drives have been hardened to deal with this workload, to the extent that Lee says the mean time between failure for surveillance drives exceeds that of conventional units.

They also outperform everyday drives in terms of power consumption, an important consideration given that surveillance drives are usually put to work in chassis alongside 4, 8, 16 or more drives. All of those drives are expected to be active, all of the time. And when surveillance recorders are switched on, all of the drives need to become active as soon as possible.

"If the start-up current requirement or ongoing power consumption is too high you can get intermittent results," Lee says. That's a no-no, so the drives use less juice when turned on and require less to keep running too.

The drives perform some other neat tricks too. The performance of large arrays can be adversely impacted by vibration as the disks start to wobble each other about. Surveillance drives are hardened against this and keep on recording video at the required rate and resolution no matter how shaky their neighbours become.

Lee says the market for these drives is growing fast, thanks to the surveillance industry moving from analogue to digital recording. He admits that volumes will never match the market for conventional hard drives, but says the opportunity is significant enough for the drives released last week to represent Seagate's second-generation product.

One thing the drives cannot do, however, is serve conventional storage needs, however tempting it sounds to put a hardened, low-power disk to work for more prosaic tasks.

"It's not recommended to put them in a conventional array," Lee says.