The new SCSI: better, faster, smaller

That old standby storage standard, SCSI, is about to get a makeover. Two technology shifts, occurring in parallel and arriving this year, will change the kinds of disk drives enterprises use up and down their storage systems.

One transformation several years in the making is the move to a new interface -- SAS (serial attached SCSI) -- which provides faster, more flexible, and more reliable connections to drives. The new spec also permits the same drive enclosure to support SAS devices and lower-cost SATA drives.

At the same time, in part due to the advent of the smaller SAS interface, 2.5-inch enterprise-class drives will start to replace tried-and-true 3.5-inch models. In the long haul this will mean that datacenters 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 midyear with internal SAS drives instead of the traditional parallel SCSI ones. Lower-end drive arrays will start using SAS drives as well toward the end of the year. “SAS is now being qualified by the major OEMs,” notes John Monroe, an analyst at Gartner. By 2008 to 2010 (estimates vary), all SCSI drives will be SAS drives.

“What IT will see is the continued trend of better capacity and performance at lower prices,” says Greg Hartzog, head of storage infrastructure at consultancy Optimus Solutions.

Although SCSI technology is changing under the hood, enterprises don’t have to worry about reworking their storage infrastructure to prepare for or manage the change. Because the drives use the same command set as previous SCSI drives, there’s no change needed to the enterprise’s storage architecture, as the SCSI command set and external interfaces remain unchanged. Also unchanged are the drives’ head assemblies, the parts that store and read the data, notes Jay Krone, director of Clariion product marketing at EMC.

“There’s not much that IT has to do,” adds Franco Castaldini, enterprise storage product manager at Seagate Technologies. “They don’t have to rip out their middleware or their storage management.”

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 minimize having multiple cabinets, some of each type, in the same location, EMC’s Krone says.

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A smaller, more flexible interface

The move to SAS dramatically changes the connection between a drive and the backplane -- whether the drive connector on a server’s motherboard or the host bus adapter within a drive array cabinet. The new connection is almost identical to the now-familiar SATA connector, and that’s intentional. 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, Optimus’ Hartzog says.