LSI Gives Limitations On DAS The Boot

A device shipping Monday could spell the end of the resource isolation and close proximity requirements of direct-attached storage (DAS) while providing an easier and cheaper alternative to SANs. Storage solution giant LSI begins shipping the SAS6160, a 6-Gbs SAS switch that permits two or more servers to share the same physical JBOD, (just a bunch of disks), RBOD (RAID bunch of disks), or other SAS resource at distances up to 75 feet.

According to Rob Callaghan, LSI's technical marketing manager, the 6-Gbs SAS6160 is an industry first. �For the first time in the SAS world, you don't have to have islands of storage, some which are underutilized,� he said. "Now you can share storage resources those across groups of servers. No one else is doing this in six gigabit."

Alacatel, Hewlett-Packard and others make SAS switches under the 3 Gbs spec, which Callaghan said lacks table routing and other capabilities of the 6-Gbs SAS spec, devices for which began hitting the channel last year. "This allows for cascading of switches and a larger number of physical drives," Callaghan said.

The 16-port SAS6160 is a half-width 1U device that can support as many as 990 drives, physical or virtual servers, switches and other connected devices at 24 Gb/s per port and 384-Gbs total throughput. Drive isolation within a JBOD is made possible thanks to new zoning rules introduced with 6-Gbs SAS spec, sometimes known as SAS 2.0.

"For example, let's say you had two servers and a couple of JBODs, one connected to each. On JBOD one, you're using 90 percent of capacity, and JBOD two is using 20 percent. I can use the zoning function to take a portion of JBOD two and make it available to server one."

Next: Zoning Creates More Connections

Zoning is implemented by SAS Domain Manager, LSI's software running inside the switch. Zoning in T10 is used to fan out connections to [create] more connections, as in a JBOD," he said, referring to the T10 technical committee, which developed the spec. �We're not inventing anything new, we're just using the 6-Gbs SAS spec.

That's significant, he said, because if a server crashes, the replacement server will recognize existing storage configurations immediately upon connection to the switch.

As a bulwark against switch failure, the LSI switches themselves support redundancy. "So if you lose one switch, you can still access the storage through the other switch," said Callaghan. Device software also implements firmware management, diagnostics and topology browsing.

Watch for a hands-on review of the SAS6160 from the CRN Test Center in the coming weeks. Listing for $2,495, the SAS6160 began shipping on Oct. 12 and is available through CDW, NewEgg and high-tech distributors. LSI also offers a two-switch, 1U rack mounting kit for $450 list.