Groups' push for hard drive compatibility questioned

A pair of industry groups have plans to make serial ATA disk drives compatible with serial-attached SCSI, but one expert raises a question: do we really need both?

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The SCSI Trade Association (STA) and the Serial ATA (SATA) II Working Group have drawn up a new deal to make serial-attached SCSI compatible with serial ATA hard disk drives at the system level.

In a joint announcement this week, the two groups said system builders will be able to use a common infrastructure and choose from a wider range of product options to meet their customers' storage requirements.

John Paulsen, spokesman for disk drive heavyweight Seagate Technology Corp., Scotts Valley, Calif., said this announcement means that future storage systems will be able to use serial SCSI interface and serial ATA interface drives interchangeably.

"This compatibility will allow a serial ATA hard drive to plug in to a serial SCSI backplane," he said.

Paulsen said a system would need to support both protocols at the firmware and driver levels to be able to use both drive technologies.

"A system integrator can choose the most appropriate hard drives [needed for a] particular application, even if that means some drives should be serial ATA and some drives should be serial SCSI on the same system," Paulsen said.

The bottom line is customers will benefit from the cost reductions the respective drive compatibility provides to backplane manufacturers, VARs and system OEMs.

"The ability to change from entry-level drives to robust, high-I/O capable enterprise drives without purchasing new systems simplifies the upgrade process and helps future-proof end user investments," Paulsen said.

All that rotates isn't gold, however.

According to one expert, there may not be a need for so many different hard drives technologies.

Marc Farley, an independent storage expert and the author of Building Storage Networks, said the days of serial SCSI drives are numbered.

"There is no clear requirement for serial SCSI disk drives. We already have serial ATA and Fibre Channel [drives]. Those two pretty much cover the requirement space already," Farley said.

The differences between SCSI and ATA drives gets smaller and smaller every year and, according to Farley, SCSI can claim slightly better performance through tagged command queuing, but the number of cases where this makes a difference is negligible.

"There is no reason a 15,000 rpm serial ATA drive could not be manufactured that would be almost as fast as a 15,000 rpm SCSI drive," Farley said. "Serial ATA will always be much cheaper and outsell serial SCSI."

He said the only place for serial SCSI is somewhere in the middle of the market. "[It's] almost certain to be a waste of money for the developers of the technology," he said.

Serial-attached SCSI and serial ATA technologies contain serial point-to-point interconnections, increased address-ability and the ability to scale to small form factors. Serial ATA drives use a phone jack-style connection, as opposed to the ribbon connector used by current ATA technology, thereby saving space. Serial ATA drives offer a throughput in the 150-180M bit/sec range.

According to the groups, a technical subcommittee made up of members of the SATA II Working Group and the INCITS T10 committee will meet to determine whether any specification changes are needed to meet the compatibility requirements.

Serial-attached SCSI systems that support serial ATA hard disk drives are expected to be available in 2004. Serial ATA systems are available now. Let us know what you think about the story. E-mail Kevin Komiega, News Writer

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