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 Introduced in 2003, serial attached SCSI (SAS) superseded the parallel SCSI interface and is widely used in datacenters where large numbers of drives are required (see illustration below).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 ?
The PS3700X serial-attached SCSI storage array provides an option for IT organizations to balance capacity and performance requirements for priority workloads such as Microsoft Exchange Server, SQL Server, Oracle databases and server virtualization projects.
SATA is slightly slower and less extensible than SCSI, Serial-Attached SCSI (SAS) and Fibre Channel drives.
Built for 10-Gigabit Ethernet and Category 7a premise wiring systems, the ARJ45 Category 7a modular plug and jack can be used as a replacement in closed-loop InfiniBand, Fibre Channel, EyeMAX, serial-attached SCSI, PCI express and microTCA applications.
A case in point is Serial-Attached SCSI (SAS), an emerging standard developed to meet the needs of mainstream enterprise-class storage systems.
The PCI Express RAID Storage Array supports 12 hot-swappable SATA or serial-attached SCSI drives, and includes an upstream host interface board and PCI Express cable.
Mark: For me, the hottest announcements were the developments in Serial-Attached SCSI.
The Monarch SAS Tester is for testing serial-attached SCSI (SAS), enterprise-class environments and devices.
Serial-Attached SCSI is the latest rebirth of SCSI and promises to greatly expand upon the existing capabilities of this enterprise storage connect.