By Dave Simpson
The SCSI Trade Association (STA) and the Serial ATA (SATA) II Working Group have embarked on an agreement that will enable Serial-Attached SCSI (SAS, or Serial SCSI) system-level compatibility with Serial ATA disk drives. This means that OEM integrators and end users will be able to plug Serial SCSI and/or Serial ATA drives into hosts equipped with Serial SCSI backplanes. It does not, however, mean that you will be able to use Serial SCSI disk drives in Serial ATA host systems (due primarily to cost and connector issues).
Serial ATA drives and subsystems are available now, but Serial SCSI disk drives and systems are not expected until some time next year (see figure).
The benefit of the agreement from an end-user perspective will be the ability to mix and match drive types in the same system enclosure. "Some users will purchase low-cost servers with Serial ATA drives, but they may also want to provision that system with Serial SCSI drives because of availability, scalability, manageability, or software support reasons," explains Harry Mason, president of STA and director of industry marketing at LSI Logic.
"End users will be able to buy one type of system and populate it with either Serial SCSI or Serial ATA drives," says Karen Flores, a member of the Serial ATA II Working Group and market development manager at Intel. "The benefit is flexibility." Flores adds that users will be able to customize systems based on application, performance, and cost requirements.
For OEMs and integrators, one of the primary benefits of compatibility between Serial-Attached SCSI systems and Serial ATA disk drives will be the ability to have a common infrastructure of cables, connectors, backplanes, cabinets, etc.
"Having the ability to populate a single system with high-performance SAS drives and low-cost SATA drives is something many [integrators and users] are anticipating," says David Reinsel, an analyst with International Data Corp. (IDC).
Serial I/O technologies are based on point-to-point connections and are expected to eventually replace their parallel predecessors.
For more information, visit www.scsita.org and www.serialata.org.
Although compatibility is generally a good thing for end users, the agreement between the two groups begs the question of why the industry will need so many disk drive interfaces in the future. Integrators and users will be faced with a confusing array of choices next year, including Parallel ATA, Parallel SCSI, Serial ATA, Serial SCSI, and Fibre Channel (see table for a comparison of Serial ATA, Serial SCSI, and Fibre Channel Arbitrated Loop).
Assuming that Serial SCSI drives ship next year, IDC predicts that those drives will account for only about 3% of total "high-end" (e.g., server) disk drive shipments in 2004. IDC expects Parallel SCSI shipments to hold a 55% market share, followed by Fibre Channel at 19%, Serial ATA at 17%, and IDE at 6%.
However, the strong trend toward Serial ATA will become clear by 2006. IDC expects Serial ATA drives to garner a 47% share of the high-end drive market in 2006, followed by Parallel SCSI at 23%, Fibre Channel at 19%, and Serial SCSI at 11%.
Although some industry observers question the need for Serial SCSI (arguing that Serial ATA and Fibre Channel cover the spectrum of requirements), IDC's Reinsel says that Serial SCSI will survive, if only because of industry perceptions.
"My bet is that SAS replaces SCSI, caps Fibre Channel [growth], and staves off SATA encroachment," Reinsel concludes.
Western Digital re-enters enterprise market
By Heidi Biggar
Serial ATA has drawn Western Digital (WD) back into the enterprise-level disk drive market. Last month, the manufacturer of ATA/IDE drives began initial shipments of Raptor, the company's first Serial ATA drive—and its first enterprise-class drive in more than three years.
"This is a huge departure for us, and it was a shock to the rest of the industry," says Steve Wilkins, director of marketing at Western Digital, which exited the high-end drive market three years ago to focus solely on desktop devices.
The Raptor drive leverages many of the key components of WD's existing ATA drives. By doing so, the company says it has been able to keep associated R&D costs down.
"While many have conceded the encroachment of ATA drives into the lower-end enterprise market, Western Digital is looking to push encroachment even farther," says Dave Reinsel, an analyst with International Data Corp.
Western Digital says its key target is the midrange server market; however, it expects initial response to be greatest among "white box" customers.
The company claims that Raptor is equal in reliability (1.2 million hours MTBF) and performance (10,000rpm, 5.2ms seek time) to competitive SCSI products, at a significantly lower cost. The drive is available in a one-platter, 36GB configuration.
Western Digital says a 4-drive Raptor configuration (with a 4-port Serial ATA RAID card from 3ware) will run about $1,039, or $7.21 per GB, compared to $10 per GB for some SCSI configurations.