STA

Author: Paul Vogt, Director of Product Marketing,
Adaptec

With Serial Attached SCSI (SAS) now widespread in the marketplace, developers have new freedom to create a single storage solution that meets a variety of price, performance, capability, and reliability needs. By having one SAS storage system meet the full spectrum of application requirements, development budgets can be reduced from previous generations where multiple products were required to meet multiple application requirements.

In addition to this flexibility, SAS offers a number of important benefits, including new levels of scalability, performance, and robustness.

Author: Willis Whittington, Senior Manager, Interface Planning,
Seagate Technology

It was clear that parallel SCSI was running out of steam when the transition from Ultra 3 (160 MB/sec) to Ultra 4 (320 MB/sec) brought with it a new terminology to articulate the technical challenges faced by the speed increase. Engineers were now forced to debate the parts and merits of a variety of "...ations" such as pre-compensation, post-compensation, equalization, packetization and skew (how did that get in there?). It was obvious that an interface technology based on the parallel transmission of data bits down a wide cable was facing a technological Armageddon and Ultra 640 SCSI would never see the light of day. Thus the SAS story began.

Six storage provider companies got together in Houston TX to discuss and float a proposal for a new serial interface to replace parallel SCSI. This new project needed a code name that would be easy to remember and eminently suitable to the new endeavor, so looking no further than the tasty local brew at their elbows, this intrepid group of interface pioneers settled unanimously on the appellation "Shiner Bock."¹

Authors: Michael Sebesta and Joseph Rebrovich
System Integration Test Lab
Hitachi Global Storage Technologies

Serial Attached SCSI (SAS) is a new serial interface for enterprise hard disk drives that will eventually replace aging parallel SCSI technology. The new serial interface provides much higher data transfer rates, improved scalability and superior reliability. SAS is also compatible with Serial ATA (SATA), which has become increasingly popular for use in nearline and entry-server applications. The SAS architecture allows IT managers to deploy either high-performance SAS or cost-effective SATA drives in the same storage enclosure, providing unprecedented design flexibility for server and storage subsystem deployments.

New storage interconnects can often present system integration challenges. SAS is no exception, although SAS' unique development approach has, in many ways, helped to minimize the challenges.

Author: David So, Strategic Marketing Manager
LSI Logic

So maybe it took a little longer than some of us forecasted or hoped. For others, maybe it happened faster than they expected. But regardless of what any of us thought back then, it is now undeniable that Serial Attached SCSI (SAS) has finally landed, and in a big way.

SAS development time-line
Initial work on the SAS specification began in 2001, as the next evolution of SCSI technology, and it was ratified as an ANSI standard specification in late 2003. The first public demonstration of SAS prototype components actually took place in July 2003. And here we are, just over three years later. During those three years, numerous companies have announced production of SAS components as well as SAS promotional and educational events.

Author: Rachelle Trent, SAS Product Manager,
PMC-Sierra

As enterprise storage requirements rapidly increase, expanding data throughput and providing scalable storage capacity is crucial. The goal of Serial Attached SCSI (SAS) was to overcome the scalability and reliability limitations of parallel SCSI and to significantly improve the ability to add hard disk drives to a system. To overcome the scalability limitation, SAS uses devices such as expanders and multiplexers (muxes).

Expanders for scalability
SAS expanders provide scalability and enable fault tolerant systems by providing multiple connections between hard disk drives and initiator devices. These redundant links between hosts and drives maintain a connection in case of a system failure. In addition, SAS expanders provide high throughput and facilitate the compatibility between SAS hosts and Serial ATA (SATA) disk drives. Expanders simplify the configuration of large external storage arrays and can be cascaded with minimal latency while preserving bandwidth for increased workloads.