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6 Gbps SATA specification ratified, but role in enterprise data storage unclear

Vendors and analysts see SAS 2.0 taking over the enterprise, but some users see a lower-cost way to boost data storage performance in the new SATA 3.0 specification.

The Serial ATA International Organization (SATA-IO) this week released version 3.0 of the Serial ATA (SATA) disk drive specification, with support for 6 Gbps transfer speeds, enhancements to native command queuing (NCQ) and power management.

Besides doubling the speed of SATA from 3 Gbps, the new spec makes several improvements to Native Command Queuing (NCQ), which prioritizes commands from host systems. NCQ will support multiple data streams and it has been optimized to better deal with contention between hosts and the disk system. Hosts will have more control over drive spin-down with the 3.0 spec instead of relying the drive's internal controls to determine when to power the drive on and off.

A 6 Gbps Serial Attached SCSI (SAS) spec was also released this spring, and vendors and analysts say 6-gig SAS will become more of an enterprise play while the SATA improvements are better suited to the laptop and desktop markets.

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"The SCSI command set just has a lot more flexibility to it, and more reliability," said Mark Noblitt, a marketing manager for disk maker Seagate Technology Inc., and member of the SATA-IO board of directors. To make the SATA spec as robust would drive up the price, which would offset the main value of SATA.

New features of SATA 3.0 are in some cases specifically geared toward consumer devices – especially the streaming support. Another new feature is support for 1.8 inch drives and small mobile devices with a new low insertion force (LIF) connector.

IDC analyst John Rydning said, "SAS 2.0 made it much more likely that broader [enterprise] applications will be enabled for SAS." Support for more distance that the signal can travel makes it more feasible to use SAS drives in a large enterprise array, as will support for encryption and 4K drive sector. The 6 Gbps transfer speed combined with those features will make SAS much more compelling, Rydning said, because SAS will finally leapfrog Fibre Channel in performance. While SATA is the cheapest of them all, Rydning pointed out, SAS still has a cost advantage over Fibre Channel. With a performance edge as well, Rydning predicted the industry will turn to SAS.

"Both SATA 6Gb and SAS 6Gb are part of the SAS 2.0 specification," Bob Fine, director of product management at Compellent Technologies Inc., wrote in an email to SearchStorage. "Though SATA 6Gb offers benefits, we really expect SAS 2.0 to be the future of the industry."

Enterprise data storage users more interested in IOPS, capacity

Some storage administrators contacted by said that with SATA, it's more important to boost physical latency and capacity in bulk disks rather than interface transfer speed. "We don't have a bandwidth issue with [SATA] drives," said David Dulek, storage administration lead for Fastenal Company Purchasing. "The heads can only do about 70 to 80 IOPS, which is our bottleneck – IOPS, not bandwidth."

David Friend, CEO of online backup service provider Carbonite Inc., which stores user data on vast arrays of SATA drives, added: "Speed is not really the issue. But we are waiting with great anticipation production shipments of 2 TB drives."

SATA 3.0 good for enterprise Flash

One place in the enterprise where SATA 3.0 is expected to play a role is in solid-state drives (SSDs).

To Dulek's point about IOPS vs. throughput, SATA-IO's Noblitt responded that the SATA spec doesn't address the I/O performance of physical devices behind the interface. But, he pointed out, "there aren't really latency issues to speak of" when it comes to SSDs, and Noblitt said he expects enterprise Flash drives to take advantage of SATA 3.0. "There's no reason for them not to," he said.

Agreed Rydning, "There isn't really demand for more performance from a data rate perspective for SATA in the enterprise – I don't think we're hitting the limits of even the three [Gbps] spec yet – but SSDs can saturate a six [Gbps] link."

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