MSA2 / MSA2000 LFF SAS Disk Drives
HP MSA2 / MSA2000 controller enclosures and large form factor expansion enclosures accept unique HP disk drive modules with different firmware and different trays than other HP storage arrays and Proliant servers. The disk drives (Options AJ737A, AJ736A, and AJ735A) have interposers attached to the back which convert the native dual port SAS interface to an SCA-40 connector. While this SCA-40 connector has the same shape as a Fibre Channel (FC) connector, the drives are NOT utilizing the FC protocol. If you look closely at the interposer, the circuitry is rather simplistic and no bridge / translator chip is attached. The interposer is, more or less, acting as a signal filter and port relocator to connect to the MSA2's proprietary backplane.
MSA2 / MSA2000 LFF SATA Disk Drives
SATA disk drive modules for the MSA2 / MSA2000 (AJ740A, AJ739A, and AJ738A) also use interposers, but they are significantly different than those found on the SAS disk drives. The SATA interposers have active logic on them that will convert a single-ported SATA disk module into a dual-ported disk module. If you look closely, you will see a MULTIPLEXER chip on the interposer which is responsible for this function. Even though the SCA-40 connector is reminiscent of a connector on a Fibre Channel disk drive, no SATA-FC bridge chip exists on this interposer.
Most modern SAS disk drives have dual ports (also known as Phys) natively. So far, SATA drives only are offered in single port configurations thus the need for the interposer. Dual ported disk drives have a separate SAS addresses for each port in a SAS fabric. Some manufacturers will argue that there are performance benefits to dual ported disk drives as well, but for the most part, it is difficult for a single disk drive to saturate a 6Gbps link. Redundancy is the key motive for adding a second port to disk drives. If you were to trace the physical paths from the MSA2000 RAID controller (down the cable connecting controller chassis to expansion chassis, into the expansion JBODs, and across the backplanes to the disk drive, you will actually see redundant physical connections to each disk drive slot.)
Dual ported disk drives are required for the MSA2 / MSA2000 RAID controllers to communicate simultaneously to disk drives (for LUNs owned by different storage processors) as well as for near instantaneous fail over during service processor failure.
The following HP Document, while not directly applicable to the MSA2000, provides a high-level overview of SAS domains and dual ported disk drives:
http://h20000.www2.hp.com/bc/docs/support/SupportManual/c01451157/c01451157.pdf
