ATA hard disks continue to make inroads into enterprise applications. ATA hard disks were once considered low-cost, relatively low-speed and low-reliability technology for desktop computing. However, StorageTek has since incorporated ATA hard disks into its storage-blade technology. Modeled after server blades, storage blades let companies add storage capacity in one rack by adding "hard disks on a board." StorageTek designed the storage-blade approach to make ATA more attractive for backup applications in larger organizations.
At the Server I/O Conference last month, ATA took another step toward being considered an enterprise-ready technology. The SCSI Trade Association (STA) and the Serial ATA (SATA) II Working Group announced they had formed a collaborative agreement to enable Serial Attached SCSI system-level compatibility with SATA hard disks. STA is a member-run consortium that supports and promotes SCSI technology. The SATA II Working Group defines, develops, and delivers SATA specifications.
The implications of the announcement for the storage community are straightforward. Storage manufacturers will have a common infrastructure in which they can develop a wide array of products appropriate for everything from very basic to highly complex storage architectures. Serial Attached SCSI and SATA drives will share connectors, cables, backplanes, and cabinets. Storage vendors and enterprises will be able to customize storage subsystems to address very specific application needs, such as performance, reliability, and total cost of ownership (TCO).
The compatibility between Serial Attached SCSI and SATA drives will also reduce the complexity of storage infrastructures, according to Marty Czekalski, vice president and director of the STA. For example, one RAID controller will be able to interoperate with both ATA and SCSI drives.
Several factors stimulated the effort to establish the new compatibility standards. Both SCSI and ATA hard disk manufacturers are incorporating serial technology. In fact, Czekalski suggested that Serial SCSI represents the next evolutionary stage of SCSI technology. In addition to SATA, Serial Attached SCSI is compatible with the Fibre Channel network protocol. Serial Attached SCSI will be introduced with transfer rates as fast as 3Gbps, although it will also support transfer rates as fast as 1.5Gbps.
ATA drives are just beginning to move to a serial protocol. Craig Lyons, a product manager at Promise Technology, which has pioneered the use of ATA drives in RAID technology, believes the move to serial will generally make it easier to use ATA drives. The ATA drives can be situated farther from the controller, and one RAID controller, for example, can interface with more drives. The thinner cabling is also easier to manage.
Officials from the Serial Attached SCSI and SATA camps argue that the technologies aren't in competition with each other. Jason Ziller, chairman of the SATA II Working Group and Intel technology initiatives manager, suggested that having one platform is better for both technologies because administrators can then redeploy and provision a mix of drives more easily.
But sharing one platform is only part of the story. ATA technology, though still not as robust as SCSI, is reaching the benchmarks necessary for enterprise readiness. In mid-February, Western Digital released a SATA drive rated at 10,000rpm and with a Mean Time Between Failure (MBTF) of 1.2 million hours. Although that still isn't as fast or reliable as SCSI drives, SATA has proved to be suitable for many applications inside large organizations. And SATA technology provides a significant price advantage compared to SCSI, which should only make SATA more desirable to large enterprises.
In the long run, the SATA-Serial Attached SCSI protocol announcement should accelerate the use of SATA technology in the enterprise. As the need for storage capacity continues to grow while IT budgets remain under pressure, storage administrators are seeking technology that can meet both their technology needs and their budgets.