New SATA Spec Consolidates, Offers Feature Upgrades

The newest Serial ATA spec consolidates all previous specifications while introducing enhancements that could give SATA drive manufacturers a better competitive stance against rival technologies.

The newest revision of the specification for Serial ATA technology consolidates all previous specifications while introducing enhancements that could give SATA drive manufacturers a better competitive stance against rival technologies while providing users with more reasons to switch to SATA-based products.

In addition to integrating the SATA specifications developed by various splinter groups over the years, the SATA Revision 2.5 specification, announced Tuesday by the Portland, Ore.-based Serial ATA International Organization (SATA-IO), offers a host of upgraded features that may provide the fuel manufacturers need to offer more feature-rich products that can compete on more even ground with SAS (Serial Attached SCSI).

One of the most significant enhancements to the SATA realm is the introduction of eSATA, a new way to use SATA external to the box. The external SATA storage solution allows users to upgrade their storage capability simply by plugging the device into the back of their systems.

"Its equivalent to a USB-based disk drive you add to your system, but its SATA that comes out of the back of the box and attaches to your external storage box," said Knut Grimsrud, president and chairman of SATA-IO.

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Another major advance is a 3G-bps speed, a doubling of the 1.5G-bps rate of the original SATA specification. The increased speed results in increased performance for SATA-based storage systems—a great selling point, said Mike Karp, senior analyst at Enterprise Management Associates of Westboro, Mass.

"3G bps gives drive vendors one more feature that increases their favorability comparison to SAS," he said. "And thats not a trivial point, because SAS and SATA drives are going into the same boxes."

Another class of upgrades involves extensions to the original SATA specification, including command queuing, hot-plugging and NCQ (Native Command Queuing), which allows multiple commands to be issued to the drive while allowing the drive to perform optimizations in the order in which it executes the commands, increasing performance.

"Hot-plugging alone is a great new feature," Karp said. "It allows users to keep an extra drive around and when something goes down, just put it in the device and youre off and running."

Other new or improved features include two new cable and connector specifications, a port multiplier that allows users to turn one SATA port into multiple SATA ports, and a port selector—a SATA-based solution for high-availability data center applications that provides the ability to create redundant paths from hosts to storage devices without creating a single point of failure.

Although many of the features arent completely new, but compiled from previous specifications or simply upgraded, consolidating everything into one specification makes it easier for designers and implementers to design products, said Marty Czekalski, interface architectures manager for Maxtor Corp., of Milpitas, Calif.

"It makes us less prone to errors, because we dont have to refer to various specifications to make sure there wasnt an errata issued to any part of the specification," he said.

Along with the SATA 2.5 specification announcement, SATA-IO released a separate specification for the Slimline Connector, a connector for swap bays on mobile PCs. The connector replaces the original SATA connector, which was slightly too large to fit into the existing envelop defined for the swap bays, Grimsrud said. The Slimline Connector specification will be rolled into the next iteration of the SATA specification, he said.

Karp sees the SATA 2.5 specification as a work in progress. Next up, he believes, will be a robust interoperability suite, similar to the interoperability environment now available for SCSI and Fibre Channel products.

"When the interoperability suite finally appears, vendors will not only be able to test against a common specification, but will be able to test in a mix-and-match environment, which will save them an enormous amount of development time," he said. "Interoperability testing can be a huge time sink and expense pit."

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