serial-attached SCSI (SAS)

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 (ANSI) 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 and magnetic tape drives

SAS 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 data transfer rate

The SAS 2.0 specification enabled a doubling of the transfer rate for SAS devices up to 6 gigabits per second (Gbps), although hardware vendors are bringing products to market that support even higher rates. LSI Corp. in 2013 started shipping controllers and SAS expanders that support 12 Gbps. Experts say the second-generation standard is expected to result in higher density SAS drives and could lead SAS to emerge as the dominant interface for networked storage.

SAS data transfer roadmap

Who uses SAS?

Serial-attached SCSI is said to offer an ideal solution for businesses with substantial storage, backup and archiving demands. SAS is widely considered to be the prevalent interface for direct-attached storage and is used to support hard drive controllers in enterprise-grade server farms.

Serial-attached SCSI vs. other interfaces

Devices that employ SAS are compatible with Serial Advanced Technology Attachment (SATA) devices. In addition, SAS products are compatible with devices that employ earlier SCSI technologies. SAS supports up to 128 direct point-to-point connections, compared to the 15-device limitation common with parallel SCSI switches. 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.

Shared SAS

Shared SAS describes a method of attaching a storage array to multiple servers. It is considered an alternative to a storage area network, offering simplified management, backup and improved utilization. Users of shared SAS storage typically include small and midsize business or project workgroups within companies.

Drawbacks to shared SAS revolve around distance limitations. Users need servers that support SAS drives or may need to purchase SAS adapters.

This was last updated in March 2015

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