SCSI to SAS

The storage standard SCSI is set to evolve. According to Gartner, by 2010, all SCSI drives will move to Serial Attached SCSI (SAS).

Due to the smaller SAS interface, 2.5 inch enterprise-class drives will start to replace 3.5-inch models. In the long haul, this will mean that data centres will accommodate more storage without eating up more floor space. Smaller drives will also reduce power usage, speed data access, and increase the overall capacity of drive arrays.

At first the changes will be invisible, with new servers coming mid-year with internal SAS drives instead of the traditional parallel SCSI ones. Although SCSI technology is changing, enterprises don’t have to worry about reworking their storage infrastructure to prepare for or manage the change. Since the drives use the same command set as previous SCSI drives, there’s no change needed to the enterprise’s storage architecture; the SCSI command set and external interfaces remain unchanged. Also unchanged are the drives’ head assemblies and the parts that store and read the data.

Older parallel SCSI drives are incompatible with SAS, so enterprises will have both sorts of SCSI devices in their DAS and SANs until the older devices are retired years from now. But that just means maintaining two types of replacement drives in case of failures, and perhaps rearranging arrays to minimise having multiple cabinets, some of each type, in the same location.

SAS controllers work with both SAS and SATA drives because the cables are both physically and electrically the same. This will allow vendors to use the same power supplies, cases and backplanes in all their products, reducing manufacturing costs and thus lowering prices to the enterprise.