Is Four-Gig Really Baked?

A key selling point for storage vendors transitioning from 2-Gbit/s to 4-Gbit/s Fibre Channel gear is backward compatibility. Customers can just replace one set of equipment with another, and everything is guaranteed to work just fine, right?

Maybe not, according to one of the key testers of 4-Gbit/s products. David Woolf, manager of the University of New Hampshire InterOperability Laboratory (UNH-IOL)-Fibre Channel Consortium, says neither vendors nor customers should take it for granted that everything will work without a hitch after a 4-Gbit/s upgrade.

There’s still work to be done,” Woolf says. “The leap is not trivial. I think 4-gig as a technology makes sense, and it is a technology that will work. But the products are brand new. People say, ‘It’s just like 1- or 2-gig, we’re just adding another speed. It’s a small change, it shouldn’t create any problems.’ But people are creating new products. You don’t want to get caught up in ‘just a little change,’ and not do the testing.”

Woolf advocates more testing on two fronts. He would like to see a third 4-Gbit/s plugfest (there have already been two, this past January and then again im May), and he might get his wish later this year. He also thinks 4-Gbit/s equipment could benefit from conformance testing.

Conformance testing tools create data patterns, modify data, insert data errors, and generate traffic to match standard 4-Gbit/s FC patterns, while sending frames within a fabric or arbitrated loop connection. Then they evaluate the device’s responses and analyze performance.UNH-IOL announced last week said it has a new Fibre Channel tester from Finisar Corp. (Nasdaq: FNSR), but only two vendors have signed up for conformance tests at the lab (see UNH-IOL Expands FC Testing ).

It's no surprise that Woolf is calling for more testing, given that testing is his job. What's more, companies pay for the conformance testing he’s talking about.

“Yeah, that’s true,” he says when that charge is run by him. “But we are a non-profit group, and it’s not like we’re trying to sell more test tools or anything like that.”

Plus, he points out, Fibre Channel had an early history of interoperability problems that required extensive testing to resolve. And if bugs are found now, it will cost less money and create fewer headaches than if they surface after products go to market.

At least one vendor doesn't consider 4-Gbit/s gear undertested. “We’re already in business with 4-gig,” says LSI Logic Corp.’s (NYSE: LSI) engineer Santanu Biswas. “I think it’s quite stable.”Besides the plugfests, there have been 4-Gbit/s interoperability demonstrations at the Storage Networking World conferences and one this week at the Intel Developer Forum (see LSI Demos Adaptors ). One of the IDF demos consists of 4-Gbit/s HBAs from , ATTO Technology Inc., Emulex Corp. (NYSE: ELX), LSI, and QLogic Corp. (Nasdaq: QLGC) in the same system, working with Brocade Communications Systems Inc. (Nasdaq: BRCD) and Qlogic switches and a Xyratex Ltd. (Nasdaq: XRTX) target.

Still, Biswas concedes 4-Gbit/s vendors could do more testing, if only to prove interoperability with emerging architectures. He expects another plugfest late this year or early 2006. That plugfest will consist of extended target and initiator tests, and it will focus more on PCI Express than PCI X.

As for conformance testing, though, Biswas says LSI and other vendors use proprietary tools to test their 4-Gbit/s devices. They don’t need UNH-IOL to do that.

Biswas says the move to 4 Gbit/s should be smoother than the one from 1 Gbit/s to 2 Gbit/s, which had its share of interoperability issues early on. “The main problem with that jump was everybody had a new SerDes,” Biswas says. “Firmware was not stable. But 2-gig has been extremely stable for a while now, and 4-gig is not a complicated jump for firmware or hardware.”

More testing could bring the proof of this that suppliers require. For now, storage vendors seem divided on the viability of 4-Gbit/s so far. At the very least, the industry is giving a mixed message. With the exception of HBAs -- where all the major players have 4-Gbit/s products -- suppliers appear conflicted about what to offer.For instance, LSI's Engenio division has a 4-Gbit/ controller that IBM Corp. (NYSE: IBM), Silicon Graphics Inc. (SGI) (NYSE: SGI), and Storage Technology Corp. (StorageTek) (NYSE: STK) sell through OEM deals. EMC Corp. (NYSE: EMC), Hewlett-Packard Co. (NYSE: HPQ), and Hitachi Data Systems (HDS) have recently launched competing systems -- still at 2 Gbit/s. Brocade has been hawking 4-Gbit/s switches and directors while its competitors Cisco Systems Inc. (Nasdaq: CSCO) and McData Corp. (Nasdaq: MCDTA) have taken their time getting into 4 Gbit/s.

The early 4-Gbit/s vendors claim they’re out with faster products because they’re ahead of their rivals' technologically. The laggards argue 4-Gbit/s has been mostly marketing hype until now (see Engenio Claims 4-Gbit/s Surge).

Either way, proving that products actually work as claimed could help some customers take the 4-Gbit/s plunge. The next question is, how many are really on the fence?

— Dave Raffo, Senior Editor, Byte and Switch