Aerial Attached SCSI (SAS)

SAS or Serial Attached SCSI is designed for transferring data to IO devices such as RAID arrays, CD-ROM drives and tape drive backup devices. This technology has evolved from the traditional parallel SCSI technology which has been used for many years primarily by the server market. SAS has been designed for the Enterprise market to meet the need for much higher data throughput, while maintaining the use of standard SCSI command used in parallel SCSI.

Serial Attached SCSI (SAS) is a computer bus used to move data to and from computer storage devices such as hard drives and tape drives.

SAS depends on a point-to-point serial protocol that replaces the parallel SCSI bus technology that first appeared in the mid 1980s in data centers and workstations, and it uses the standard SCSI command set. SAS offers backwards-compatibility with second-generation SATA drives. SATA 3 Gbit/s drives may be connected to SAS backplanes, but SAS drives may not be connected to SATA backplanes.

The T10 technical committee of the International Committee for Information Technology Standards (INCITS) develops and maintains the SAS protocol; the SCSI Trade Association (SCSITA) promotes the technology.

Serial Attached SCSI Advantages

• Reduced signaling overhead
• Elimination of bus contention
• SAS does not require termination as in traditional SCSI
• SAS eliminates the problem of clock skew
• The total number of devices allowed is increase from 32 with parallel SCSI to 16384 for SAS.
• SAS supports data transfer speeds of up to 6 Gbps.
• SAS supports SATA devices.

Serial Attached SCSI (SAS) is a method used in accessing computer peripheral devices that employs a serial (one bit at a time) means of digital data transfer over thin cables. The method is specified in the American National Standard Institute standard called Serial-attached SCSI (Small Computer System Interface), also known as ANSI/INCITS 376-2003. In the business enterprise, serial-attached SCSI is especially of interest for access to mass storage devices, particularly external hard drives.

Serial Attached SCSI offers advantages over older parallel technologies. The cables are thinner, and the connectors are less bulky. Serial data transfer allows the use of longer cables than parallel data transfer. Problems related to crosstalk are less likely in serial interfaces than in parallel interfaces, because there are fewer conductors in the cables. The hardware for serial interfaces is less costly than the hardware for equivalent parallel interfaces.

SAS offers data transfer rates in excess of 3 gigabits per second (Gbps) with potential rates of 10 Gbps or more. Serial-attached SCSI is said to offer an ideal solution for businesses with substantial storage, backup, and archiving demands.

Devices that employ SAS are compatible with serial ATA (Advanced Technology Attachment) devices. In addition, SAS products are compatible with devices that employ earlier SCSI technologies. External disk drives, host adapters, and expanders were the first devices to employ SAS. The technology is expected to expand to printers, scanners, digital cameras, and other peripherals.