Storage: A New SCSI Standard

Previous advances in small computer system interface (SCSI) technology have often been yawners for all but the purest storage afficionados: a little bandwidth boost here, a few extra gigabytes there, a tad more performance every now and again. But in 2004, a new SCSI standard, called Serial Attached SCSI (SAS), promises to take the venerable storage technology to a new level?or at least empty some systems of all that cable clutter.

SAS replaces old-style, inches-wide wire ribbons with thin connectors, similar in size to an Ethernet cable. The obvious benefit to the new design is improved airflow through ever-shrinking system enclosures. But the slim pathway doesn’t mean reduced performance. The new standard supports throughputs of 300MBps (similar to Ultra320 SCSI’s 320MBps) with plans for 600MBps capability waiting for an update to the spec next year. Reduced connector size will allow for far smaller drives, suitable for server blades and other tight quarters, such as laptops.

One of the most interesting new additions will be SAS’s compatibility with Serial ATA drives. SATA drives are currently available but offer lesser performance and reliability compared with SCSI. They are, however, significantly less expensive per gigabyte. Upcoming SAS adapters will let users add SATA drives to an SAS system to match their storage needs. Using one adapter, a server could contain a few dozen SAS drives for the most critical data and another collection of lower-cost SATA drives for backup, archive and less critical uses, with the adapter automatically determining what type of drive is attached (SATA adapters, however, will not do the same thing for SAS drives).

The SAS specification was slated for final approval by the T10 group of the InterNational Committee for Information Technology Standards before the end of 2003. Products based on the standard are expected to ship by the middle of next year.