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IT departments seem to have an unquenchable thirst for storage capacity -- a thirst that's not being adequately satisfied by standard-issue storage enclosures.
"Even though disk drives are getting bigger, the huge demand for data hasn't been met by them," says Alan Johnson, director for product application engineering at controller and enclosure manufacturer Infortrend. Among data growth's worst offenders are applications such as backup-to-disk and HDTV, he says.
Why not just daisy-chain more enclosures for more capacity? "Space is often at as much of a premium in the computer room as the storage itself," says Johnson. "The days of huge, air-conditioned rooms are going away," he says, giving way to an era of "space constraints and 19-inch racks."
Put another way, IT managers simply won't put up with storage that requires more physical resources. "IT managers would probably be pretty mad if companies tried to sell them devices that needed a lot more space, power and cooling," says Franco Castaldini, enterprise storage product manager at Seagate.
Nevertheless, Infortrend probably won't try and stuff more than 24 drives into 4U, at least for now. "After 24 drives, you start to run into some serious issues," Johnson says. Cooling is one problem, as is rotational vibration. With I/O-intensive applications such as transactional databases, the rotational vibration caused by several drives moving around independently can cause adjacent drives to spontaneously recalibrate themselves, he explains.
However nasty rotational vibration might be, it hasn't stopped enclosure manufacturer Xyratex from building a denser array. This spring, Xyratex announced its 4835 enclosure, which holds 48 drives in a 4U box, or 12 drives per U. Assuming the latest generation of 500 GB drives, that's 24 TB of capacity in less than seven inches of rack space. Xyratex's most notable OEM partner is Network Appliance, which private-labels all of its Xyratex enclosures.
However, Xyratex engineers freely admit that designing the 4835 wasn't without its challenges. "It was a small engineering nightmare," says Steve Thompson, Xyratex's CTO. "The worst thing you can put next to a disk drive is another one right next to it."
Copan Systems is another vendor that makes dense arrays. Its Revolution 200T stuffs 896 drives in a single cabinet just over 48U high, or 18.66 drives per U -- quite possibly the densest array on the market.
To keep power and cooling costs down, as well as to prolong drive life, the Revolution is built around a massive array of idle disks (MAID) architecture, which spins down drives that are not in use, explains Roger Archibald, Copan's VP of marketing and business development. Only 25% of the system's drives can be active at any one time, and drives in a RAID set are not adjacent to one another to reduce rotational vibration issues.
Furthermore, if a drive sits idle for more than 30 days -- a distinct possibility in archive environments -- Copan performs "disk aerobics," whereby it spins up the drive and checks to see if the data written on it is still good. "With disk aerobics and power management, we can extend the life of the drive for a very long time," Archibald says.
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