Small disks, big specs


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2.5-inch HDDs
Now that 2.5-inch drives offer higher capacities, they appear destined to become the next enterprise storage standard. "You've got a small size, high performance and high capacity," says EMA's Karp. "You can put a lot of these drives in one box and still draw less power." The initial 2.5-inch enterprise drives will spin at 10,000 rpm, but Karp expects 15,000 rpm versions to follow. It's the same story with capacity. The 2.5-inch drives jumped from 146GB to 300GB by mid 2008, but Karp sees them hitting 500GB pretty quickly.

In June, Seagate Technology LLC announced a 2.5-inch enterprise-class drive with impressive specs: 300GB capacity, 10,000 rpm, 60% greater density than 3.5-inch drives, a 6Gb/sec interface, 1.6 million hour mean time between failures (MTBF) and drive-level full-disk encryption.

As the HDD industry struggles to generate low-cost IOPS, 2.5-inch disks combined with faster performance will play a key role. More spindles packed into the array spinning at faster speeds mean more IOPS. And forget about topping out at 15,000 rpm. "With the 2.5-inch drive you can get 20,000 rpm," says Chris Wood, CTO at Sun Microsystems Inc.'s storage and data management practice. As of this writing, no commercial 20,000 rpm drives had been announced.

On top of greater IOPS, the 2.5-inch drives will consume far less energy, even when spinning at 20,000

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rpm. "You've got a smaller head and a smaller platter. That gives you a big gain in space and energy," declares Wood. "The industry has reached the tipping point for 2.5-inch drives."

Hawaiian Electric, however, isn't ready to jump at arrays built around 2.5-inch drives for its enterprise storage. "We see 2.5-inch drives for servers," says the firm's Watanabe. For now, the company will stick with the 3.5-inch standard for enterprise storage, at least until the industry standardizes on 2.5-inch drive enterprise arrays.

The Research Foundation of the State University of New York at Albany will pass on 2.5-inch drives, too. "We have a Sun [StorageTek] 9990 SAN and until 2.5-inch disks fit into that we're not interested," says John Busdiecker, director of infrastructure services. As for 6Gb/sec performance: "For us, that's overkill now, although it might be of future interest," he adds.

Energy savings
The new disk drives save energy in several ways:
  • Large 3.5-inch drives (1TB and above) mean fewer spinning disks are required for the same capacity. They also spin at slower speeds.

  • 2.5-inch drives have lighter platters and smaller heads, which require less energy (9W vs. 13W); some laptop drives consume just 1.8W.

  • Future control of spin speed will enable selective slowing or stopping of individual spindles to save more energy.

This was first published in September 2008

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