Electronic Design

12-Gbit/s SAS Pushes The Storage Envelope

SAS (Serial Attached SCSI) dominates the enterprise, which always needs more storage—and faster storage. The 12-Gbit/s SAS standard will help deliver faster performance, and PMC-Sierra is poised to give users that advantage with a line of chips that covers controllers, SAS expanders, and RAID-on-Chip (RoC) silicon. The faster interface speed is especially important for flash storage, which was pushing the bounds of 6-Gbit/s SAS and SATA.

Designed for external storage systems, PMC-Sierra’s Tachyon SPCv-12G protocol controllers push the processing limit past 2 million IOPS and double the throughput compared to the current 6-Gbit/s SAS generation. The chips are available in eight- and 16-port versions and support PCI Express Gen 3 x8 interfaces.

The family also supports integrated StorClad encryption technology, which features line-rate AES-XTS encryption. This enables the use of standard, non-encrypting drives while providing a more secure operating environment. Additionally, the chips support wide-port target mode and the Enterprise T10 DIF data integrity field.

SAS expanders are the typical method for connecting a large number of drives to a controller. PMC-Sierra’s SXP-12G SAS/SATA expanders are available in 24-, 26-, 48-, and 68-port versions. They can handle 3G/6G SAS/SATA devices as well as 12G SAS devices plus optical SAS with very low switch latency.

The expanders also support 4K SAS addresses. The high-density 48- and 68-port versions allow a single chip to handle an entire system while a pair provides redundant access to the array. An on-chip MIPS processing core boosts system performance and handles physical-layer (PHY) power management. A 10/100 Ethernet media access controller (MAC) interface provides out-of-band management support.

Meanwhile, the SRCv-12G RoC chips incorporate the latest host, drive, and memory interface standards. The DDR3 2133-MHz memory controller provides a battery-backed cache. Also, the RoC chips have a PCI Express Gen 3 x8 interface and are available in eight- and 16-port versions. They support 1.5G/3G/6G SAS and SATA interfaces along with 12G SAS interfaces. Hardware RAID acceleration support handles RAID 0, 1, 5, 50, 6, and 60 configurations.

Expect PMC-Sierra’s chips to show up in the company’s Adaptec host bus adapters in the future. This is one area where the new, proposed Mini-SAS HD connectors may come into play.


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