Serial SCSI Promises Faster I/O in Servers

Computerworld - An IT standards body is close to ratifying a new serial interface specification for SCSI disk drives that's expected to speed up I/O throughput in servers and could eventually challenge Fibre Channel technology's share of the high-end disk array pie.

The serial-attached SCSI specification is expected to be approved during the second quarter by the T10 technical committee of the Washington-based International Committee for Information Technology Standards. Disk makers such as Seagate Technology LLC and Maxtor Corp. last week said they plan to begin shipping serial SCSI drives to system vendors by year's end.

The IP-based technology will support faster I/O throughput than the current parallel SCSI interface does, said Gordy Lutz, a product marketing manager at Scotts Valley, Calif.-based Seagate.

Serial SCSI is expected to replace its parallel predecessor as the standard disk-drive interface in most servers as well as in workstations and low-end to midrange disk arrays, according to John Lohmeyer, the T10 technical committee's chairman.

Drive's Advantages

But the new drives will also offer faster I/O speeds than Fibre Channel devices do, Lohmeyer said. And like Fibre Channel technology, serial SCSI drives will have dual I/O ports for fail-over purposes and will support simultaneous send-and-receive operations.

Seagate, which makes about 95% of the Fibre Channel drives used in high-end disk arrays, said it expects serial SCSI and Fibre Channel to complement each other. But Milpitas, Calif.-based Maxtor is betting on serial SCSI to replace Fibre Channel disk in five to 10 years.

Because the specification supports point-to-point connections between disks and controllers through the use of so-called extenders, there should be no competing demands to slow down the flow of data, as there are on conventional system buses, said Brendan Collins, director of product marketing at Maxtor.

Lev Gonick, CIO at Case Western Reserve University in Cleveland, said the ability to open up the internal bandwidth of servers is serial SCSI's greatest potential feature for improving his school's operations.

Mark Price, director of enterprise architecture at Carlson Companies Inc., said serial SCSI will become interesting to the Minneapolis-based travel industry conglomerate "at the point when the cost of it becomes equal to or less than what we're currently using."

Carlson now uses a Fibre Channel storage-area network (SAN) with multiprotocol switches made by San Jose-based Nishan Systems Inc. to connect mirrored data centers over IP. But, Price said, "we think Fibre Channel is probably a shorter-lived technology. It's very expensive and complicated to implement."

Serial SCSI will likely become "an alternative to doing Fibre Channel in [SANs], but it's not the panacea," said Jamie Gruener, an analyst at Gartner Inc. in Stamford, Conn. "It's meant to replace parallel SCSI. It's not meant to be a complete replacement of everything."