Author: Debika Ingham
With the advent of any new interface, users of the technology invariably ask, “Now what do I have to buy?” And perhaps more importantly, “What existing investments have been protected?” The transition to Serial Attached SCSI (SAS) will ensure many levels of investment protection, both during its initial stages and long thereafter.
At an application command level the transition to Serial Attached SCSI is transparent. Such transparency derives from SAS’s fundamental role as a new transport for existing SCSI commands; as such it must serve as a direct replacement for the parallel SCSI interface.However, at the driver level there are several required changes (similar to those needed during previous transitions in SCSI technologies). Primarily these involve the new serial connectivity and new devices within that topology, entailing an additional level of functionality to analyze and configure the SAS domain, as well as utilize the many new features provided by the protocol.
Connectors and Cables
The serial interface that Serial Attached SCSI employs requires different cables and connectors than those used by previous SCSI generations. While there are many advantages to these cables–fewer signals, few power pins, smaller form factor, etc.–they do present a barrier to plugging older technology SCSI drives into SAS domains. An interim solution may be bridging products/adapters that enable SAS connectivity with its parallel predecessor. Of course, the serial SCSI interface has been specifically designed to ensure compatibility with another serial technology, Serial ATA (SATA). In concert with SAS-standard keyed connectors, SATA drives will directly plug into SAS backplanes. Maintaining this component level compatibility delivers unprecedented investment protection to component manufacturers, OEMs, and end users alike.
Beyond compatibility, Serial Attached SCSI also maintains a high degree of interoperability between different vendors’ components. Results from a recent SAS plugfest confirm that widespread interoperability has indeed been achieved, ensuring SAS systems will not be confined to a particular vendor’s solution.
The Migration Path and Broader Infrastructure
The transition to Serial Attached SCSI will first be delivered in clients via discrete components (typically add-in cards), thus enabling end users to attach either parallel SCSI or SAS disks. As broader adoption of SAS follows, more highly integrated and embedded solutions will emerge, employing controllers integrated with processing power and connectivity directly on the motherboard. Throughout this process SAS clients won’t impact existing infrastructure for the network, either in terms of IP and Fibre Channel connectivity or their required switch/route infrastructure.
SAS Backwards Compatibility and Long-term Roadmap
One of the most compelling reasons to transition to Serial Attached SCSI is the long-term roadmap it will provide for increased bandwidth and more flexible connectivity, all the while maintaining compatibility from one generation to the next.
Kelly Woods, Susan Bobholz and Bob Sheffield contributed to this article.