SCSI going serial

Have you had a chance to take a look at the new SATA (serial ATA) drives and RAID controllers? You'll appreciate SATA's point-to-point, slim, independent connections between controllers and disk drives.

Although interesting, SATA solutions are no match for high-performing and very reliable SCSI siblings, which are still the cornerstone of enterprise storage, challenged at the high end by Fibre Channel.

However, that familiar scenario is about to change: SCSI as we know it -- with its parallel architecture; fat, expensive cables; and often challenging setup -- is about to be replaced by a new point-to-point protocol named SAS (serial attached SCSI). SAS promises faster performance, unrivaled flexibility, and thinner connectors, while maintaining software compatibility with its predecessor. Get ready to say goodbye to the old SCSI and its termination woes, and to welcome new devices based on SAS in the near future.

Recent news from Adaptec, announcing cooperation with major drive manufacturers to deliver SAS solutions, gave me the opportunity to converse with Linus Wong, director of I/O marketing at Adaptec's Storage Solutions Group, who estimates that products based on the new protocol will be available by spring of next year.

These two emerging protocols, SAS and SATA, have much in common. Take, for example, the departure from the parallel interface for the single bit data path. This facilitates delivering higher transfer rates and shrinking the size of cables and connectors. Interestingly, SAS controllers will also support SATA drives, bringing much welcome flexibility to storage vendors and customers. Furthermore, both SATA and SAS are point-to point protocols, hence each connection is unaffected by other devices on the same controller.

Nevertheless, don't let those similarities with SATA sway you. SAS is in a class of its own when it comes to performance, scalability, and reliability. If you are still struggling to position SATA in the enterprise storage jigsaw puzzle, SAS specs by contrast command a "prima donna" role.

In fact, the first instance of SAS will support full-duplex 3Mbps, with the second generation expected to double that speed, firing up the competition with top-performing Fibre Channel drives.

In addition, disk vendors will welcome the tiny form factor of the SAS interface, because it facilitates moving to smaller (2.5-inch), faster-spinning disk drives and building devices having dual host connections.

Factor in the ability to address a great number of devices (initial deployments will stop at a Fibre Channel-teasing 128), support for as many as 6 meters of out-of-the-box connections, and room for further growth, and you have a protocol that will probably carry the SCSI flag across the enterprise storage for years to come.

Adaptec estimates that by 2006 the enterprise landscape will see only SATA, SAS, and Fibre Channel new entries, with serial storage taking the lion's share. How will you cage that beast in your company?

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