SAS: now and in the future

Computer Technology Review, July, 2004

Serial Attached SCSI is the logical evolution of SCSI, including long-established software advantages and the Serial ATA electrical and physical connection interface. With enterprise storage requirements escalating and becoming more complex, factors such as larger capacity, greater density, security, scalability and accessibility are more critical than ever. To look into the issues revolving around SAS, the SCSI Trade Association convened a roundtable to answer questions posed by CTR editor-in-chief Mark Ferelli.

When are SAS systems going to be on the market?

Wong: My expectation is that the components will be coming together and be very robust by Q3 and Q4. And then you'll start to see products from system vendors be available in the beginning of 2005.

What is the pacing item that will govern the introduction of SAS-specific products in the marketplace?

Wong: I think the pacing item is just the interoperability and qualification that needs to go through the OEMs. So again, the plugfests of the components suppliers have gone very well. The components are coming together very well. And I think the pacing item is just the testing and qualification to get these into products and released to the market.

Croteau: Two things are happening fast. One, I think the way that the specification is being put together intelligently to utilize some of the work that's already been done in SATA, to leverage that into the interoperability, is helping get SAS product to the market faster than we benchmark it against similar products--such as Fibre Channel or iSCSI--pick your favorite technology from the last decade or so. The second is that really new technology deployment in the market is two-phased. The first will be discreet product, just as we normally do, so Linus referenced himself as a component supplier. Certainly we have others in the SCSI Trade Association. And those products will start to show up towards the second half of this year. And then the large scale of the ramp will really target the next server refresh cycle. And that's why the 2005 time-frame really looks like the bread and butter of SAS deployment. But right now, just based on interoperability and just based on the early plugfest data, I would say it's well ahead of several other new technologies. If you look at it just because of all the investment that we're utilizing, it's driver models SCSI command structure and then all the serial work that's been done on the status side with regard to buys and cabling, etc.

I'd like to draw an analogy with iSCSI for just a moment. One of the things that is pacing the introduction of iSCSI into the marketplace is the lack of iSCSI targets. There are initiators all over the place, but targets are just coming to market. How target-rich an environment is SAS now, and what is the road map to get to a more target-rich environment?

Schilling: Well, assuming that you could classify disk drive as a target, we're pretty rich with targets with really all drive suppliers having announced support for SAS and, to varying degrees, delivering product or plans to deliver product.

What level are the targets going to be? Are we going to stick to things like disk and tape drives or automation?

Croteau: I think if you look at SCSI deployment historically, any device that's utilized SCSI is--and will be--a candidate for SAS just based on the evolution of spec. And I think comparing it with iSCSI, while they do share some of the fundamental common command structures, iSCSI's really just a transport, a method to get to a box. Whereas, when we talk about SAS, we're really talking about the fundamental connection of the hard drive and the host connectors. In fact, I wouldn't be surprised if you didn't see combinations of iSCSI in fabric to SAS. But SAS is not dependent on fork-lift upgrades, etc., for value propositions like the iSCSI camps have made. It's a natural evolution of the technology and continues SCSI well into the future.

Wong: What Chris said is important. There is a fundamental difference between iSCSI and SAS--which is that SAS is just the next generation of SCSI. We're going from Ultra 320 SCSI, parallel SCSI, to 3-gigabit-per-second serial SCSI. iSCSI isn't just the next evolution of Fiber Channel, it's an alternative technology to create a storage area network (SAN). And the value proposition needs to be defined. The usage models need to be identified. Is it a DAS replacement? Is it an entry-level SAN? There are a lot more unknowns in the iSCSI environment and iSCSI world. Those unknowns don't exist for SAS; SAS is just there instead of Ultra 640.

Then we see SAS as the next evolution of SCSI. What benefits are our readers--who are dominantly systems integrators--going to experience from instituting a SAS capability within their organizations?

Schilling: One might be the idea that a SAS backplane or system is not only compatible with SAS disk drives, but SATA disk drives. So it will provide significant flexibility for your readers, integrators and users to design and develop a common backplane that can be proliferated across different applications with the ability to chose drive type based upon application and use it on that common backplane.