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Serial Attached SCSI switch holds promise for SMBs

Apr 03, 20063 mins
Data CenterIBM

Flexibility, ease of use seen putting off the need for Fibre Channel SANs.

A new switching technology, Serial Attached SCSI, is catching the attention of server vendors and industry experts for its ability to network more storage devices than SCSI and preserve user investments in direct-attached disk drives.

LSI Logic this week is expected to demonstrate a 1U (1 ¾-inch-high) 36-port SAS switch at Storage Networking World in San Diego. The switch lets users join as many as 10 host computers to a few JBODs (just a bunch of disks) that contain existing SAS or serial Advanced Technology Attachment (SATA) disks. Using such a technology may let companies put off migration to iSCSI networks or more expensive and complex Fibre Channel storage-area networks (SAN).

“SAS switching is primarily a mid-tier answer for connecting multiple servers to an inexpensive storage system with inexpensive [copper] infrastructure,” says Randy Kerns, an independent storage analyst. “This will be popular at the end of the year.”

The components necessary for enabling SAS-switched fabric networks consist of servers that contain a SAS storage interface – most new x86 servers do – and a storage controller (the intelligence in the storage array) that uses a chipset supporting SAS. IBM and HP are among the vendors that have SAS-enabled their servers: the xSeries and ProLiant, respectively.

SAS is the replacement for the Ultra320 SCSI interface. Ultra320 SCSI is a parallel interface that offers only 14 connections between servers and storage devices. SAS allows for as many as 128 connections in the LSI Logic implementation.

LSI Logic and PMC-Sierra last year introduced switch chips for use in storage controllers, which HP and IBM say they will incorporate into controllers by the end of this year.

Both chip manufacturers have garnered a lot of attention for their technologies. IBM says it will use the PMC-Sierra chipset for networking its BladeCenter servers to storage. HP also has an active campaign by SAS-enabling its ProLiant servers last year, and this year the company claims it will support SAS switching via an external switch. Its storage controllers, too, will have SAS switching capability.

SAS should be considered an alternative to iSCSI or Fibre Channel networking, observers and analysts say.

“There is [a small and midsize business] market for SAS-based switches for connectivity between servers, something the Fibre Channel and iSCSI folks don’t want to hear,” says Greg Schulz, analyst for StorageIO.

Fibre Channel will be necessary for distances greater than about 52 feet, because SAS supports only that much space between servers and storage. However, experienced and expensive IT help is needed to manage, deploy and maintain Fibre Channel SANs. Many customers who need distance and ease of use and deployment will choose iSCSI because it operates like the Gigabit Ethernet they are accustomed to.

For SMB customers, however, SAS switching will represent an opportunity for enlarging their storage network. They have been working with SCSI connections for the past 20 years and are familiar with it. Being able to use existing and inexpensive ATA or SATA drives is attractive to them.

“SAS could be a more attractive data solution, in that you already have someone that understands the SCSI protocol,” says Levi Norman, group marketing manager at HP. “The management of Fibre Channel itself requires a higher than average cost and more complex management experience than many customers have today.”

LSI’s SAS switch lets multiple storage domains be configured, and is ideal for rack-mounted or workgroup server and storage environments. An embedded Web server will provide switch management. The switch is expected to be available from system OEMs such as IBM and HP this fall.