SAS Powers Ahead!

Author: Marty Czekalski, Vice President, SCSI Trade Association
Interface and Emerging Architecture Program Manager, Seagate

At the recent SCSI Trade Association (STA) SAS Solutions Open House in San Jose, Marty Czekalski discussed the past, present, and future of SAS. He went through the SAS roadmap, briefly describing 3Gb/s SAS origins, 6Gb/s SAS highlights, planned enhancements to 6Gb/s SAS, and the outlook for 12Gb/s SAS. In addition, he discussed the capabilities these technologies enable in delivering solutions to end customers.

The first SAS Plugfest was in 2004, when industry participants worked together to ready 3Gb/s SAS products for the market. The initial SAS releases focused on preserving the legacy SCSI infrastructure and enabling SATA in the environment. Since then, 3Gb/s SAS products have become widely accepted. Now, the storage industry is moving forward and getting ready to bring out a major upgrade from 3Gb/s SAS to 6Gb/s SAS. The first official 6Gb/s SAS Plugfest will be held at the end of this year. However, at the SAS Open House, 6Gb/s prototype hardware is being demonstrated by several industry providers working together. 6Gb/s SAS, with backward compatibility for 3Gb/s, will quickly become a key interface in the storage world. But even as 6Gb/s SAS is getting ready to be introduced to the market, plans are being formulated for 12Gb/s SAS in the late 2012 timeframe.


Figure 1: SAS Roadmap


What is 6Gb/s SAS-2? It is more than just the transfer speed. While the T10 standard allows for many optional features, the SCSI Trade Association is defining a specific set of features to be branded along with the 6Gb/s SAS logo. Besides the 6Gb/s transfer rate, the features include cabling improvements to allow up to 10-meter cables, standardized expander zoning, and spread spectrum clocking to reduce radiated emissions (EMI). There is also an optional feature – multiplexing. Multiplexing allows multiple slower speed data streams to be aggregated into a 6Gb/s data stream. So an expander can multiplex two legacy drives, each running at 3Gb/s and provide a single 6Gb/s data transfer upstream. It is an efficient way of aggregating bandwidth. Multiplexing was included as part of the Open House 6Gb/s demonstration.

These enhancements provide a base on which to build new capabilities. Features such as the Data Integrity Field (DIF) where 8 bytes of protection information per sector is used by the drive and host system to validate the data, features like Full Disk Encryption (FDE) for security or improved external storage capabilities and features like virtualization that takes advantage of the high-interface bandwidth – all of which are enhanced by SAS-2. All of these features combine to allow for bigger, more function-rich computing environments.

Beyond 6Gb/s SAS-2, there are additional enhancements planned for the 2011 timeframe – currently referred to as SAS 2.X. The main focus is improvements to support additional scaling. This includes cabling schemes that would allow copper cables of 20 meters or more. Optical cabling is also being considered for even longer cabling distances. Power management options that would bring SATA-style power management into the SAS environment are under discussion.

When these enhancements are added to 6Gb/s SAS – providing even longer distances, larger infrastructure support, and improved power management capabilities – it allows for larger data system scale-outs and also generally greener storage. It helps to accommodate the design of subsystems to take advantage of things like Massive Arrays of Inactive Disks (MAID). These are large drive configurations where some of the drives are powered down until they’re needed. Power will be managed in a more proactive manner than is currently typical. The features in SAS 2.X will help establish it as the premier interface for storage interconnection.


Figure 2: SAS Growth


In 2012, 12Gb/s SAS is coming…

SAS has quickly overtaken SCSI as the key high-end storage attachment interface. With significant improvements in speed and features it will become even more capable as a storage interconnection interface. And it will continue to expand and improve over time.

Marty Czekalski has over twenty years of senior engineering management experience in advanced architecture development for storage and IO subsystem design, ASICs and memory systems. He is currently Sr. Staff Program Manager within Seagate’s Enterprise Market Development Group.

Marty’s previous industry experience includes engineering management roles at Maxtor, Quantum and Digital Equipment Corporation. Additionally, at Digital Equipment Corp., he was a member of the Storage Strategy Task Force and the Next Generation IO Task Force, setting the directions for storage and interface strategy. Mr. Czekalski was a founding member of the Serial Attached SCSI Working Group that led to the development of Serial Attached SCSI.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.