serial attached SCSI (SAS)
Serial Attached SCSI( SAS) is an interface technology for high-speed transfers. Since with the parallel Small ComputerSystem Interface (SCSI) the synchronization of the parallel data streams becomes more and more complicated with increasing transfer rates, serial data transfer offers itself as an alternative.
SAS technology, which is backward compatible with SCSI and has been standardized by ANSI, has a data rate of 150 MB/s in the first version, which has been increased to 300 MB/s, 600 MB/s and to 1.2 GB/s in the course of development.
Serial Attached SCSI offers software compatibility with SCSI, lower cost connectors, better scalability, higher data transfer rates, and supports SATA hard drives. SAS operates in duplex mode and uses the same connectors as Serial ATA (SATA). However, the data port also uses pins on the back of the connector, bringing two ports to each hard disk drive, allowing redundant architectures.
The internal connection cables can have a cable length of 1 m, while the external connection cables can be up to 10 m long, making them suitable for connecting external peripherals. Up to 128 devices can be addressed via an expander; connection is via a SATA storage switch, which can be used to branch from one input port to up to 127 device ports.
Communication with peripheral devices is supported by several protocols. These include Serial Management Protocol( SMP), Serial SCSI Protocol( SSP), and SATA Tunneling Protocol( STP). The Serial Management Protocol is used to connect the hard disk drives in a point-to-point connection. Up to 16,384 devices can be addressed via one port. The Serial SCSI Protocol allows controllers to communicate with SAS devices and with SCSI software.
Since all SAS controllers support the SCSI protocol and Advanced Technology Attachment (ATA), SATA hard disks and SAS hard disks can be connected to one hard disk controller.