Insider: 4-Gig's Successor Uncertain

Sales of 4-Gbit/s Fibre Channel gear are expected to dominate the SAN market for the next five years, but there is a bit of confusion about what will come next, according to the latest Byte and Switch Insider.

The report, 4-Gbit/s Fibre Channel SANs: A Market Update, maintains that the expected move to 8-Gbit/s Fibre Channel as a next step after 4-Gbit/s faces several roadblocks. First, there is a question about whether current standard copper-based twisted-pair cabling can handle the higher transmission rate over more than 25 meters. The move to 8-Gbit/s may require more expensive cabling, which would eliminate one of the biggest drivers of the current transition from 2-Gbit/s to 4-Gbit/s price parity.

"As with most types of cabling, the distance capability tends to decrease as the data transmission rate increases," research analyst Martin Courtney writes. "Single-mode fiber is well equipped to handle long distances, but the higher dispersion rate in thicker multimode fiber can cause problems. It is not yet clear if 8-Gbit/s transmissions can be extended to 100 meters without adding new transceivers, which is likely to push up the cost of 8-Gbit/s components."

Courtney also points out that transmission engineers and cabling standards bodies have time to work out a way to keep costs down. But that's not the only issue regarding a move to 8-Gbit/s Fibre Channel.

The report says the Fibre Channel Industry Association (FCIA) standards group is hedging its bets with two sets of specs. The Base2 Fibre Channel specs double the capacity each time, allowing the jump from 2- to 4- to 8-Gbit/s and so on, while remaining backward compatible. However, the FCIA also has a Base10 specification for 10-Gbit/s Fibre Channel and perhaps 20-Gbit/s down the road.The problem with Base10 is that the spec is not compatible with Base2, so organizations cannot merely plug 10-Gbit/s Fibre Channel devices into existing SAN infrastructure. The entire infrastructure would have to be upgraded, a costly process.

Why bother with Base10? Because with iSCSI about to get a bump from 10-Gbit/s Ethernet, Fibre Channel would be in danger of losing its performance advantage.

"With the issues about cabling and backwards compatibility affecting 8-Gbit/s and 16-Gbit/s, this could be the point at which many organizations are forced to make decisions about switching from Base2 to Base10 Fibre Channel architectures, or even abandoning Fibre Channel altogether and moving to a complete iSCSI-based 10-Gigabit Ethernet SAN," Courtney writes.

Courtney concludes the FCIA has a sound strategy for keeping SAN adopter on the Fibre Channel track, but advises customers and vendors to keep options open. "Nothing is ever certain in the IT industry," he writes. "The wiser vendors will keep a close eye on buying patterns and be ready to meet whatever challenge comes their way."

The report also profiles 4-Gbit/s vendors and a complete rundown of their 4-Gbit/s gear.Companies analyzed in the report include: