Serial Attached SCSI

Serial Attached SCSI comprises three transport protocols:

Serial SCSI Protocol (SSP) — supporting SAS disk drives.

Serial ATA Tunneling Protocol (STP) — supporting SATA disks.

Serial Management Protocol (SMP) — for managing SAS Expanders.

For the Link and PHY layers, SAS defines its own unique protocol.

At the physical layer, the SAS standard defines connectors and voltage levels. The physical characteristics of the SAS wiring and signaling are compatible with and have loosely tracked that of SATA up to the present 6 Gbit/s rate, although SAS defines more rigorous physical signaling specifications as well as a wider allowable differential voltage swing intended to support longer cabling. While SAS-1.0/SAS-1.1 adopted the physical signaling characteristics of SATA at the 1.5 Gbit/s and 3 Gbit/s rates, SAS-2.0 development of a 6 Gbit/s physical rate led the development of an equivalent SATA speed. According to the SCSI Trade Association, 12 Gbit/s is slated to follow 6 Gbit/s in a future SAS-3.0 specification.

July 29, 2011

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