Silicon Rolls For SAS In Server Blades

SAN JOSE, Calif. — The Serial Attached SCSI interconnect will branch out beyond use as a link to hard drives this week with the announcement of two new parts from PMC-Sierra Inc. that aim to make SAS a storage fabric inside server blade systems.

To date, 3-Gbit/second SAS has been a storage interconnect for servers and hard-disk arrays at the middle of the technology spectrum, between the high-end Fibre Channel and the entry-level IDE and Serial ATA alternatives. But a handful of companies, including PMC-Sierra and LSI Logic Corp., have talked about SAS as a storage switching fabric inside systems.

"You can expect all SAS expander companies, including LSI Logic, to support SAS fabrics that can be used to implement [storage networks inside server] blades," said Harry Mason, a director of industry marketing at LSI and president of the SCSI Trade Association, which oversees the SAS spec. "I think you will find some differences in the feature sets, and there could be some functional variations, but we'll be doing plugfests to make sure that they all conform to whatever [ANSI] approves."

PMC worked with Hewlett-Packard Co. to define an access control mechanism for SAS. The new feature aims to stop malicious attacks, such as denial of service, and to isolate storage from computer traffic and provide other levels of VPN-like security. The duo's approach is implemented as a zone control table managed by an embedded controller on an SAS expander/switch that stores policies for up to 128 device groups.

In May, PMC and HP proposed their implementation to the American National Standards Institute. A working group is now pushing the concepts forward under a proposed SAS-2 specification.Meanwhile, PMC has rolled out its first silicon supporting the approach. The 24- and 36-port PM8399 SXP 24x3GSec and PM8398 SXP 36x3GSec devices will sell for $59 and $89 respectively, in lots of 10,000. That price is expected to significantly undercut the costs of implementing Fibre Channel, Infiniband or Gigabit Ethernet fabrics for storage inside server blades.

No protocol conversion

A move to SAS would also save the costs of protocol conversion, required when Ethernet carries the storage traffic. However, the blade backplanes — which today generally run Gigabit Ethernet — would need to be rated to support 3-Gbit/s SAS traffic.

By moving to SAS, designers can potentially leverage into a system fabric their existing investment in SAS controllers coming in next-generation server blade adapters. However, they will have to add an SAS blade to their systems — an additional cost for chassis based entirely on Ethernet. "We have a handful of early-adopter design wins. People like the concept of staying in the SAS protocols for a broader part of the blade architecture," said Mark Stibitz, vice president and general manager of PMC's Enterprise Storage Division. "You will basically have a SAN [storage-area network] running on the SAS protocol."

The two new PMC chips come in 27 x 27-mm CSBGA packages and are fabricated in 0.13-micron technology.0