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Serial Attached SCSI (SAS) Technology

Practical like Serial ATA and powerful like SCSI: SAS alias Serial Attached SCSI combines the benefits of two established technologies. The result is flat cables, uncomplicated connection possibilities and minimum downtimes ? together with a protocol which does not become a bottleneck even in complex server environments.
What is Serial Attached SCSI?

Serial Attached SCSI is a new SCSI interconnect specification being developed to address future storage I/O requirements. It will leverage the cost economies of the Serial ATA physical interface and connector while preserving the robust software and hard disk drive reliability of SCSI. Serial Attached SCSI offers key advantages over the parallel SCSI standard to present a viable continuation of the SCSI roadmap.

Serial Attached SCSI opens up many new possibilities: SATA and SAS disks can be run together on one single adapter (left). Thanks to dual-porting, two hosts can have access to one disk (middle). Expanders enable multiple SATA or SAS disks to be connected to one port.

What markets will Serial Attached SCSI serve?

By offering performance and reliability equivalent to today's SCSI disk drives, Serial Attached SCSI has broad application in workstations, servers and external storage. It also offers a convergence path with Fibre Channel in the future.

What's the difference between Serial Attached SCSI and Serial ATA?

Serial ATA is cost-optimised for the desktop as a direct replacement for EIDE. Adaptec expects Serial ATA hard disk drive performance and reliability to match that of today's desktop drives. Pricing for enterprise-class Serial Attached SCSI drives is expected to be no higher than today's SCSI and Fibre Channel drives.

Will servers use Serial ATA or Serial Attached SCSI?

SCSI still dominates the mainstream server storage market. Parallel SCSI and Serial Attached SCSI will continue to provide the most value for enterprise applications where reliability, availability and scalability are key requirements.

Over the past two years, EIDE penetration into the cost-sensitive sub-entry server market has increased, a trend expected to continue with Serial ATA. Serial ATA offers enhancements relative to EIDE, but remains inappropriate for enterprise environments.

Does Serial Attached SCSI affect the market for Ultra640 SCSI?

Yes. Adaptec expects Serial Attached SCSI to replace Parallel SCSI over time. Whether or not customers deploy Ultra640 depends on the timing of Serial Attached SCSI product availability.

Does Serial Attached SCSI affect the market for Fibre Channel?

Yes. Fibre Channel offers unique features such as support for up to 16 million devices and dual-ported disk drives, and remains appropriate for complex SAN applications. Serial Attached SCSI's point-to-point architecture expands the connectivity of SCSI, enabling Serial Attached SCSI to address the needs of multi-initiator environments more effectively than parallel SCSI.

What are the key user benefits of Serial Attached SCSI?

Serial Attached SCSI offers the following key user benefits:

What will the price of SAS be like compared to parallel SCSI, Serial ATA, and IDE?

It is expected that the cost of a SAS end-to-end solution will be similar or lower in price to parallel SCSI.

SAS technical specifications

Technical specifications Serial Attached SCSI
Performance Full-duplex with
Link aggregation
(wide ports @ 24 Gb/sec)
3.0 Gb/sec (at introduction)
(6.0 Gb/s planned)
Connectivity 8-metre external cable
128 devices
Expanders
(16K+ total devices)
SAS to SATA compatibility
Availability Dual-port HDDs

Multi-initiator point-to-point
Driver model
 Software transparent with SCSI


Roadmap to SAS technology: