Storage Management Strategies for the CIO
The SCSI Trade Association
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(STA), an industry association established to support and promote SCSI technology, has spent much of the last three years developing Serial Attached SCSI (SAS) technology and finalizing and standardizing the specifications for it. Along they way, they have conducted a number of "plugfests" and now claim that SAS is ready for prime time. Indeed, a few manufacturers are already starting to offer SAS-based products. For example, Maxtor and LSI have recently completed compatibility testing of the Maxtor® Atlas® SAS hard drive family and LSI Logic SAS host bus adapters, expanders, RAID controllers and ASIC initiators; and, they are now offering a SAS bundle product. The power and performance of the large SAS system tested at the most recent plugfest "matched expectations and the SATA compatibility test at 3 gigabits per second (Gbps) was highly successful," according to Harry Mason, president of STA and director of Industry Marketing at LSI Logic. Indeed, compatibility with SATA is shaping up to be one of the most critical features of SAS.
STA has done everything it could to develop and prepare SAS for the storage market, according to Mike Karp, a senior analyst for Enterprise Management Associates. For instance, he says, STA made SAS and SATA physically compatible and integrated selected features from other storage standards to create a highly functional storage interconnect. "System builders now have a single technology base on which they can efficiently build a flexible set of products that will appeal to just about every tier of storage," he says.
It''s a big plus that SAS can be used side by side with SATA, leveraging the strength of each, says John Webster, analyst at the Data Mobility Group. "You can use a common controller for both and allocate the data with high performance/throughput requirements to SAS and the data with lower performance requirements to SATA," he says. What''s more, he points out, is that you can even pull a SAS drive out of an array midplane and replace it with a SATA drive if you want.
For people "still struggling with parallel SCSI cables" Webster says SAS offers tremendous flexibility as well as performance (3 Gbps/drive) and reliability (dual porting). "SAS almost lost the battle for market before they started until they made one brilliant move," says Arun Taneja, founder and consulting analyst for the Taneja Group, Hopkinton, Mass. He says the brilliant move was to redefine SCSI as a serial architecture, which removed the cabling distance limitations inherent in the traditional parallel interface, and, in addition, they made the physical interface identical to SATA. That meant designers could choose freely between SAS and SATA.
"I'm very aware of all the activities among vendors that are doing SAS-based products and I can say there is a huge amount of money being spent on SAS to make sure it has a place in the IT infrastructure," he says. However, Taneja says while some early products are almost ready, server motherboards with the SAS interface probably won't arrive until early in 2006. Then, as the new year progresses, SAS should gain significant momentum.
And is there a down side to SAS? "I don't often say this but if there are risks to migrating from parallel SCSI to SAS, I don''t see them," says Webster. Furthermore, SAS technology eliminates "the proverbial rat's nest" of iSCSI cables. The bottom line, says Webster, is that there are now more choices for the enterprise -- FC, SATA and now SAS.
"In fact," he adds, "I don't really understand why SAS didn't happen sooner."
For more information:
Make way for serial-attached SCSI
Serial Attached SCSI gains momentum
About the author: Alan Earls is a freelance writer in Franklin, Mass.
This was first published in December 2005
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