The New Reality: Serial Attached SCSI Becomes Available
Author: Linus Wong
Director, Strategic Marketing, Adaptec
Serial Attached SCSI (SAS) leverages the 20-year evolution of the SCSI protocol, carrying forward its trusted reliability and stable feature set. Since its inception three years ago, SAS has promised new levels of scalability, flexibility, and cost-effectiveness for connectivity, data transport, and data storage.
The announcement of the first prototypes in 2003 marked a major milestone in the transition from drawing board to mass market availability. Since then, the first generation of technologies and products that will bring the benefits of SAS into the enterprise have been developed and tested, and a variety of integrated solutions have been demonstrated at numerous venues.
Interoperability testing was essential to the development of SAS, which increases flexibility with an architecture that supports both SAS and Serial ATA (SATA) disk drives and components. SAS products are compatible with other vendors' SAS products, and also work with existing and next-generation SATA products. Testing conducted throughout 2004, including three plugfests at the University of New Hampshire InterOperability Laboratory, successfully demonstrated all the required interoperability in a variety of SAS products and configurations.
The same companies that pioneered SCSI and continue to invest in its development as a reliable standard that meets evolving technology and functionality requirements, are the force behind the creation of SAS. Industry support comes from all of the major disk drive vendors, host adapter suppliers, chipset manufacturers, large computer makers, and many other suppliers.
SAS Controllers and Adapters
RAID controllers and host bus adapters (HBAs) provide the computing power and connectivity that underlie the SAS architecture. For internal and external storage configurations, they determine RAID capabilities and maximum data speed, and enable servers and workstations to connect to high-performance storage.
Four- and eight-port 3Gb SAS controllers are currently available that incorporate RAID for data protection. As of this writing, the highest performance controllers and HBAs deliver 4.8GB/second maximum throughput.
SAS Disk Drives
SAS provides unmatched flexibility in enterprise-class solutions, allowing a single storage system with a common backplane to incorporate multiple types of disk drives. Depending on its needs, an enterprise can cost-effectively support online transactional workloads with SAS drives and increase near-line/secondary storage capacity by deploying cost-effective SATA drives.
At this time, new 2.5" 10,000 revolutions per minute (RPM) SAS disk drives will have maximum sustained data rates of approx. 62 MB/second. These small form factor drives will be available in 36GB and 73GB capacities. In the 3.5" form factor; 10,000 RPM SAS drives will be capable of up to 90MB/sec and 15,000 RPM drives will approach 100MB/sec maximum sustained transfer rates. Capacities in the 3.5" form factor will be available in up to 300GB and 147GB respectively.
Expander chips act as a switch to simplify configuration of large external storage systems that can be easily scaled with minimal latency while preserving bandwidth for increased workloads. Each edge expander connects up to 128 SAS or SATA devices and a fan-out expander can connect up to 128 edge expanders to provide addressability to a maximum of 16,256 end devices.
SAS expanders also maximize performance in the enterprise environment, and allow individual links to be combined to create wide ports, enabling system designers to aggregate the performance of Serial Attached SCSI initiators and expanders to increase total available bandwidth.
3Gb/s SAS expanders are currently available in 12-port models, although other sizes, from nine to 36 ports will soon follow.
SAS subsystems offer both SAS and SATA drive compatibility for easy expansion of direct attached (DAS) and fabric attached storage (NAS/SAN). The subsystem can be used to build high-availability systems that feature no single point of failure, and support highly reliable and scalable connections such as multi-node clustering for automatic failover availability or load balancing, a topology that is vital for mission-critical applications.
The unique SAS architecture can scale to meet the throughput requirements of virtually any enterprise and enables organizations to standardize on a single server or storage system for a wide range of application requirements.
SAS Cables and Connectors
SAS cables and connectors offer the best of both worlds: complete SATA compatibility with the scalability, performance and ease of SAS. These connectors and cables are smaller than previous generations and allow for less intrusive cabling at distances up to 10 meters equalized, with faster throughput and dual-port connectors.
SAS products are now ready to be integrated by OEMs, VARS, and enterprises into a variety of storage solutions. Even the most bandwidth-intensive and transaction-heavy applications will benefit from the advanced flexibility, greater scalability, and next-generation performance that SAS provides.
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