serial attached SCSI

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serial attached SCSI

A standard hardware interface for storage drives. Introduced in 2003, serial attached SCSI (SAS) superseded the parallel SCSI interface and is widely used in datacenters where large numbers of drives are required (see illustration below).

SAS drives are generally faster than SATA drives and more reliable, but are also more costly. Although SATA drives can be connected to a SAS interface, SAS drives require an adapter to hook up to a SATA controller (see SATA and SATA Express).

SAS is a point-to-point architecture that uses a controller (host bus adapter) with two full-duplex channels that operate simultaneously. Each channel (SAS port) transfers data at 3, 6 or 12 Gbps in each direction. In contrast, the consumer-oriented SATA interface has only one channel.

SAS Protocols: SSP, STP and SMP
The Serial SCSI Protocol (SSP) is used for SAS drives, and the Serial ATA Tunneling Protocol (STP) is employed for SATA drives. Expanders use the Serial Management Protocol (SMP). See SCSI and hard disk interfaces.

Massive Scalability
SAS channels (ports) can connect to a single drive or to an expander that connects up to 128 drives (or host bus adapters). A Fanout Expander can connect Edge Expanders, and one system can support 16,256 drives.

Dual Ports for Fault Tolerance
SAS drives use the same form factor as Serial ATA (SATA) for the cable connector but add a second port for connection to two controllers or expanders for fault tolerance.
References in periodicals archive ?
By combining Serial Attached SCSI technology and the small 2.
PMC-Sierra and Adaptec have addressed customers' needs with a low cost, proven turnkey Serial Attached SCSI architectural solution for the growing tiered storage systems market," said Mark Stibitz, vice president and general manager, Enterprise Storage Division at PMC-Sierra.
Adaptec has always ensured the interoperability of its controllers with a broad range of components and disk drives and will do so with its Serial Attached SCSI adapter, an 8-port solution that delivers industry-leading data transfer rates and storage configuration flexibility.
Serial Attached SCSI will also lower complexity by providing a common storage platform for mission critical and business critical storage.
The Serial Attached SCSI specification defines a device-level enterprise storage interface incorporating SCSI backward compatibility, serial point-to-point interconnections, dual porting, increased addressability and the ability to scale to small form factors.
Serial Attached SCSI, the successor technology to the parallel SCSI interface, leverages proven SCSI functionality and promises to greatly build on the existing capabilities of the enterprise storage connection.
SAN FRANCISCO -- SCSI Trade Association (STA) is introducing the new Serial Attached SCSI (SAS) Advanced Connectivity Roadmap which previews the connectivity advances to support future SAS growth in the enterprise.
Serial Attached SCSI is the logical evolution of SCSI, including long-established software advantages and the Serial ATA electrical and physical connection interface.
SCSI Trade Association (STA), in its effort to promote the understanding and use of Serial Attached SCSI (SAS) technology, is presenting a tutorial at the Storage Networking World (SNW) Conference, Thursday, April 9, from 11:15 a.
This exclusive roundtable was held May 28, 2004 on Serial Attached SCSI (SAS) with emphasis on the special plugfest session for SAS/SATA interoperability on June 23-24 at the University of New Hampshire, I/O Lab.
Read worldwide, SSW is STA's free Serial Attached SCSI (SAS) e-newsletter.
The back-end interface would be agnostic and support SATA, SATA-II, Serial Attached SCSI (SAS), or Fibre Channel allowing for new technologies but also the mainstay of the storage industry (Fibre Channel).