A New Landscape for Disk

Since SATA drives became a viable option about three years ago, choosing a drive for networked storage has been fairly simple. There was Fibre Channel for the highest performance and reliability, and SATA for high capacity and low cost.

Now those choices are getting more complicated. Serial attached SCSI (SAS) systems are moving up the food chain into networked storage, mainly because, unlike their parallel SCSI predecessors, SAS can run in the same arrays as SATA. The SAS/SATA combination places high-performance SAS and low-cost SATA as two tiers in the same system.

Then there's FATA, which has been kicking around for two years and is slowly finding its way into more systems. FATA is a hybrid combining a Fibre Channel interface with ATA drives, which makes it an alternative to SATA. Fibre Channel and FATA drives can sit side by side in a system as a two-tier rival to SAS and SATA.

"We're seeing drives go down parallel tracks," says analyst Greg Schulz of StorageIO Group. "Until now you've had Fibre Channel for performance and SATA for price and capacity. Now that's being split down the middle. On the Fibre Channel side, you're seeing Fibre Channel and FATA together and on the SATA side there's SATA and SAS."

When SAS was developed, the conventional wisdom held that it would be primarily used for low-end storage and servers rather than as an enterprise alternative to Fibre Channel. That's still how LSI Logic, the top seller of SAS components, sees it. (See LSI Rolls SAS for DAS and LSI Launches SAS.)"We don't see SAS replacing Fibre Channel," says Bruce Grieshaber, product manager for LSI's SAS HBAs. "Fibre is in the SAN and will stay there. We see SAS in systems for SMB or scalable DAS. With parallel SCSI, you couldn't scale across servers. SAS lets you scale storage pools across servers."

Not everybody sees SAS limited to servers. While Dell and smaller vendors Infortrend and Promise have shipped SAS-enabled DAS systems, they expect to have networked SAS storage arrays at some point in the future. At least two iSCSI vendors, EqualLogic and StoneFly, plan to launch SAS IP SANs later this month to let customers use high performing drives along with cheaper SATA disk.

Fibre Channel and SAS both spin at 15,000 RPMs and support capacities up to 300 Gbytes. SATA and FATA have slower spin times (up to 7,200 RPM) and larger capacity (up to 750 Gbytes). SAS and SATA cost less because they ship in higher volumes.

Still, Fibre Channel clearly isn't going away and FATA drives could gain popularity in time. IBM became the third major vendor to offer FATA drives last month when it added them as an option to its enterprise DS8000 and high-end midrange DS6000 systems. (See IBM Addresses High End.)

IBM hasn't abandoned SATA, though. The storage systems it sells through OEM deals with LSI's Engenio and Network Appliance offer SATA drives. IBM disk storage brand manager Craig Butler says SAS is on the "long term roadmap" for the DS4000.EMC takes a similar big bucket approach, except it calls FATA low-cost Fibre Channel. Its Clariion midrange systems support Fibre Channel, SATA, and FATA, while its enterprise Symmetrix systems use Fibre Channel and FATA, and its entry level Clariion AX150 is SATA-only. (See EMC Makes Good on DMX-3 and EMC Uncages 4-Gig Clariions.) An EMC spokeswoman says the company is "evaluating the reliability, performance, and interoperability of SAS drives" before deciding whether to add them to its product portfolio.

Hewlett-Packard, which coined the FATA term, offers FATA and Fibre Channel but not SATA in its EVA midrange platform. 3PAR also sells FATA with Fibre Channel in enterprise and midrange systems, but no SATA. Other vendors such as Hitachi Data Systems and Network Appliance offer Fibre Channel and SATA without SAS or FATA.

For all the talk about drives, storage customers don't seem to be giving them much thought yet. Roger Cass, CTO of Cincinnati, Ohio-based healthcare firm MediSync, considers all the different drive types mostly a matter of vendor marketing.

"If you say I can buy SAS, SCSI, or a hybrid drive that does SATA or Fibre Channel, my answer would be, 'I don't care, does it work? Is there a super speed improvement?' If the answer is no, it's just a drive sitting on the server," he says.

Cass says drive types dont matter much to him because "we put a pair of mirrored SCSI drives in a server. We store an operating system on top of that, and move all the important data to our array. It's a non-issue then. The array hides me from the drive in there."He admits others might look at it differently. MediSync runs an EqualLogic iSCSI SAN with SATA. "We don’t have any investment in Fibre Channel," he says. "If I just spent $70,000 on this huge Fibre infrastructure, I want stuff that plugs into that."

The University of Wyoming has considerable money invested in its IBM DS8100, and director of systems services Bob Morrison says he likes the idea of using FATA drives. "We're interested in looking at the new tiered storage options with FATA," he says, but he acknowledges he has no immediate plans to add them.

— Dave Raffo, News Editor, Byte and Switch

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