SAS/SATA array leverages PCIe

By Dave Simpson

On the surface, the latest addition to JMR’s BlueStor line of disk arrays appears to be a “me too” SAS/SATA subsystem. Features of the 3U RAID array include 16 SAS or SATA drives for up to 16TB of capacity with SATA drives or 4.8TB with 15,000rpm SAS drives.

But under the covers the system has a key differentiator: In addition to directly attaching to hosts via the PCI Express (PCIe) bus, the system uses PCIe as a storage expansion interconnect in a “pseudo-SAN” configuration that can theoretically scale up to 4,096 disk drives (4PT of capacity with 1TB SATA drives) using PCIe switches. The use of the PCIe bus eliminates the need for bridges or conventional interconnects such as SCSI, SAS, Fibre Channel, or InfiniBand.

Why PCIe? “It’s the widest bandwidth transfer mechanism available,” says Steve Katz, JMR’s vice president of sales, “and direct attachment to the PCIe bus is as close as you get to that bandwidth. The other advantage is that you can keep adding storage using serial PCIe switches until you saturate the PCIe bus.”

The latest addition to JMR’s BlueStor line is the PCIe X8 (eight lane) Expansion RAID subsystem. The company claims single-chassis performance of 1.4GBps in a test configuration that included an Intel S5000PSLSATA motherboard with two dual-core 3GHz Xeon processors and 2MB of memory, two Atto Technology R348 RAID controllers/adapters, 16 15,000rpm SAS drives from Fujitsu, and 2MB sequential read operations in a RAID-0 configuration. In a RAID-5 configuration with two eight-drive RAID arrays and 2MB sequential reads the array achieved more than 1.2GBps throughput. (Full benchmark results are available at www.jmr.com.)

Katz notes that in the tests the system averaged about 87.5MBps per drive, which comes close to the maximum transfer rate (100MBps) for the 15,000rpm SAS drives.

The PCIe X8 RAID array is the successor to JMR’s first-generation X4 implementation (which clocked in at about 2GBps with 48 drives). The X8 subsystem has been shipping to JMR’s channel partners for about two months, with general availability slated for early October. An X16 implementation is expected at about the same time. (The Gen 2 X16 PCIe bus has a bandwidth of 16,000MBps.)

The systems are based on JMR’s PeSAN (PCIe Storage-attached Network) technology and can be attached to the company’s BlueStor Storage Server or any other PCIe-based host. In addition to Atto’s controllers, the BlueStor arrays have been tested with SAS RAID controllers from vendors such as Adaptec, AMCC/3Ware, Areca, and LSI. Options include X8 and X16 internal PCIe switches and 6-port or 12-port external switches.

JMR quotes pricing of less than $1 per gigabyte.

This article was originally published on August 01, 2008