Will SAS 2.0 grow greener storage?

SAS 2.0 is more than just sheer speed

FC, SCSI, SAS, SATA ... the alphabet soup of different connectivity protocols for disk drives can be confusing. Why do we have so many? The simple answer is because new technologies like SATA and SAS pop up fast, old technologies like SCSI do not disappear as quickly.

Multiply those protocols for the two basic drive formats (2.5-inch and 3.5-inch), add the various capacities available, and you have a richness of choice like never before.

In time, we should see some of those protocols fade away if not disappear completely. Consider, for example, this chart that Gautam Mehandru, product marketing manager at PMC-Sierra, presented during our recent conversation. Take a look at IDC's projection of SAS units shipped: According to the study, the overwhelming majority of SAS drives shipped over the next few years will be of the 2.5-inch ilk, while FC and SATA protocols will take the lion's share of 3.5-inch shipments.

What will make SAS more popular in the near future? SAS 2.0, according to PMC-Sierra. "SAS 2.0 brings new life into SAS and makes it attractive for the enterprise systems," explains Mehandru. Then he anticipates my next question, adding that "the reliability numbers are pretty high for these 2.5-inch drives."

The new version of the SAS protocol -- which "should be signed off in the next couple of months or so" -- has many improvements.The most visible of these is its doubling of the transfer rate to 6Gb per second.

However, SAS 2.0 is more than just sheer speed. Features like zoning should give SAS-based networked storage the ability to isolate segments, similar to what admins can do with FC. Having cable lengths up to 10 meters may seems ludicrous compared to the stretch of FC or plain Ethernet, but it's still an improvement over the previous 6-meter limit.

All of this should make SAS 2.0 compare well with the popular 4G FC and should tease major storage vendors into embracing the new protocol, but what's PMC-Sierra's stake in this?

As you may have already guessed, the vendor just announced a new protocol controller for SAS 2.0. The PM8000 Tachyon SPC 8x6G -- the first to be produced for SAS 2.0, according to PMC -- joins PMC-Sierra's family of FC and SAS controllers. "PMC is pretty dominant in that space [FC controllers]; we have 70 percent market share," says Mehandru.

It's nearly impossible to take a good picture of a chip, but this diagram should give you a good idea of how the new Tachyon works. And as this image shows , the controller will be mounted on a card having the proper interface to the host system.

What can we make of this intoxicating look at the upcoming SAS 2.0? I expect to see storage systems based on 2.5-inch drives that take up less space, consume less energy, and produce less heat while delivering faster (or at least equal) performance and better reliability than today's tier 1 arrays. If PMC's expectations of lower TCO are correct, customers could even save some money -- for a change.

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Mario Apicella

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