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Two routes to tiered storage

Internally tiered storage--a shelf of low-cost disk in an otherwise expensive storage system--is all the rage with storage buyers. To wit: Twenty-five percent of the total number of terabytes shipped in 2004 by storage array maker Engenio was in the form of SATA drives, says Steve Gardner, director of product marketing. This represents a tenfold increase over 2003.

But how to engineer that inexpensive tier is a debatable issue among storage vendors. One option is to plug cheap and plentiful SATA drives into an existing Fibre Channel (FC) chassis by way of FC-to-SATA protocol conversion hardware, typically bridge or router chips. Alternatively, a vendor might align with Seagate and adopt its inexpensive FC drives.

At this time, the industry seems to be going down the bridge/router path, as exemplified by Sierra Logic's SR-1216 router, which allows an FC disk enclosure to accept SATA drives. As of last month, Dot Hill (supplier to Sun Microsystems), Engenio (supplier to IBM, SGI and StorageTek) and Xyratex (supplier to Network Appliance) were all Sierra Logic customers. Sierra Logic has also announced its BR-2401 family of silicon bridges, which allow a single SATA disk drive to emulate a single Fibre drive.

FC-to-SATA bridge and router chips allow vendors to reuse their existing FC chassis, but add only "a few tens of dollars" per drive to the cost of the SATA drives, says Bryan Cowger, VP of marketing at Sierra Logic.

Seagate's line of nearline disk drives, the forthcoming NL35 family, also has its advocates, namely Hewlett-Packard and Xiotech. Compared with generic SATA drives, the NL35 family is designed for nearline--not desktop--applications, says Peter Steege, Seagate's senior global product marketing manager. That means they're designed for always-on conditions and provide enhanced error- recovery control features.

The biggest problem with Seagate's approach isn't the technology, per se, says Arun Taneja, senior analyst at Taneja Group, Hopkinton, MA. It's the fact that its the only drive manufacturer to offer such a product. As a storage OEM, "there's no way I want to be beholden to a single company. With [the NL35 drive], I'm basically at Seagate's mercy," Taneja says.

Thus far, Seagate doesn't see that as an overwhelming obstacle to NL35's adoption. "We see a real need and our customers say they see a real need," says Steege. Enough need that "they'll be interested even though it's just us."

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