The arrival of the first 2Gbit/s Fibre Channel storage products should provide better interoperability for storage area networks (Sans).

Increased capacity may also help IT managers at firms suffering San congestion.

With the latest generation of 2Gbit/s products, manufacturers say they have improved both interoperability and price/performance. One incentive for manufacturers to improve their products is that there are now competing technologies on the horizon. The principal challenger to Fibre Channel is iSCSI and the promise of storage networking over Ethernet.

"Fibre Channel is maturing. The industry has realised there are basics that everyone has to conform to - 2Gbit/s products show that Fibre Channel is not standing still waiting for iSCSI to catch up," says Joe Kimpler, director of business alliances at switch and host adapter specialist QLogic.

QLogic was the initiator of the 2Gbit/s Fibre Channel Developers Consortium. "The consortium brings together all the big players and sets directions," says Kimpler. "We all support 2Gbit/s and will move towards a common standard."

Doubling speed

For storage suppliers, 2Gbit/s is a logical step forward. Mike McNamara, product marketing manager for storage subsystem developer Eurologic, says: "It is really just a doubling of speed."

Some manufacturers have combined 2Gbit/s technology with other innovations to cut costs. For example, Qlogic's 2Gbit/s switches will be cheaper than its 1Gbit/s models because instead of the four-port chips of the previous switches, it has a single 16-port chip.

The 2Gbit/s technology offers a relatively small speed increase in an industry used to tenfold jumps in network performance. But if 2Gbit/s equipment costs no more than 1Gbit/s products and can be used with existing 1Gbit/s Sans, it is likely to attract buyers. Backwards compatibility has been built in, so a 2Gbit/s device should work at 1Gbit/s or 2Gbit/s, depending on what it is connected to.

The main use for 2Gbit/s Fibre Channel components, at least initially, will be as a backbone linking islands of 1Gbit/s Fibre Channel equipment.

This relies on switches carrying out speed negotiation on a port-by-port basis, so a 2Gbit/s port that detects a 1Gbit/s device will drop its transmission rate to 1Gbit/s. In the original Fibre Channel Arbitrated Loop architecture, everything within a loop had to run at the same speed, but Fibre Channel switching makes it possible to have zones running at different speeds, all attached to the same switch.

Congestion

The need for faster San backbones has been growing. Many users have responded by assigning multiple ports or host bus adapters (HBAs) to a single link, but this causes problems, according to Paul Talbut, chairman of the Fibre Channel Industry Association Europe.

"1Gbit/s is enough for most applications, but if you connect San clusters together you get congestion, so most people use parallel links," he says.

While 2Gbit/s Fibre Channel should alleviate congestion on inter-switch links, it may be less helpful in providing servers with faster San links. The problem is that today's PC-based server architectures are not up to the task, according to Mark Woodford, a technical pre-sales consultant at enterprise storage integrator Posetiv.

A 64bit PCI bus running on a server at 66MHz is capable of 500MB/s data transfer rates, he says. A full-duplex 2Gbit/s Fibre Channel can carry up to 400MB/s, perhaps less in real use but enough to ensure that a single PCI bus cannot saturate more than one 2Gbit/s host adapter.

Enter Arapahoe

This means that a typical server with two PCI buses will merely move from four 1Gbit/s connections to two 2Gbit/s links. "Doing more than just reducing the card count will require Arapahoe," Woodford says.

Arapahoe is the codename for the next-generation of expansion bus architecture after PCI and PCI-X. Unlike InfiniBand, which connects servers to external switches, Arapahoe will be inside the server.

InfiniBand could also solve the problem, as InfiniBand switches could be connected to San gateways. Indeed, the first InfiniBand implementations are likely to be for processor area networks or server farms - for example, with blade servers connected to a switch that connects to Fibre Channel or iSCSI storage.

Plug and play

While some vendors have introduced 2Gbit/s abilities to new equipment, others already had partially 2Gbit/s-capable equipment. Eurologic's McNamara said his firm introduced a 2Gbit/s backplane for its Sanbloc array last year, and has shipped 2Gbit/s Fibre Channel disk drives from Seagate for some time.

"It wasn't much of a technical challenge," he says. "We just changed the I/O modules and port bypass circuits to 2Gbit/s. We have around 4,000 Sanbloc products that can be upgraded by swapping modules."

However, while 2Gbit/s may see initial success in the inter-switch backbone, there will probably be less need for it at the storage device level, where 1Gbit/s already provides enough capacity. McNamara expects to see wider uptake of 2Gbit/s next year, once Eurologic begins shipping I/O modules that also support Raid.

The ability to combine 1Gbit/s and 2Gbit/s Fibre Channel in a single switched fabric will encourage acceptance, as will compatibility with the faster versions of Fibre Channel planned for the future.

The 2Gbit/s Fibre Channel is likely to be succeeded by a 10Gbit/s version that will use the same transceivers, fibres and transport layer as 10Gbit Ethernet. In the meantime, 4Gbit/s Fibre Channel is still on the roadmap and may appear as a subsystem architecture.

Seagate's strategic marketing director, Dave Anderson, says the firm hopes to start shipping 4Gbit/s-capable drives in 2003. "We don't know if 4Gbit/s will be needed, but that's what the technology allows us to do," he says. These drives will use a copper interconnect within the subsystem.

Outside the subsystem, 10Gbit/s Fibre Channel could then take over, carrying four signals multiplexed over a single fibre. However, it could be 2005 or later before this technology is widely available.

Anderson adds that though Seagate's Fibre Channel disk drives do not fully utilise their 2Gbit/s interfaces today, this will change. "We are at 70MB/s off the drive today," he says. "A conservative projection says we'll exceed 100MB/s before long."

Product differentiation

Though the physical problems of Fibre Channel interoperability are being dealt with in the 2Gbit/s generation, manufacturers still want to differentiate their products. They plan to do this by adding proprietary features in areas such as security and the programming interfaces that link software to hardware. The result might be that the basic link between a switch from one vendor and a HBA from another would work, but in each server firms might need to run vendor-specific software for HBA failover, for instance.

If this happens, the compatibility difficulties will have moved from the physical layer to the San management level. "In general, we all plug and play at the physical layer," says McNamara. "Getting solutions to work in virtual environments, and software tools to manage all the platforms and products, those are still being defined."

In the long term, the management problems should be solved, enabling all kinds of storage to interoperate seamlessly, including iSCSI and Fibre Channel. In the short term, the 2 Gigabit Fibre Channel Developers Consortium is planning an event in association with other storage industry groups, to demonstrate that Fibre Channel really does plug and play.

It looks as if 2Gbit/s will enable Fibre Channel to maintain its lead over iSCSI for some time to come. As Fibre Channel developers point out - and most of them are also developing iSCSI products - getting decent performance out of iSCSI will require hardware acceleration of TCP/IP, which will put the cost up.

www.posetiv.com
www.seagate.com
www.qlogic.com
www.eurologic.com

SUMMARY

• 2Gbit/s Fibre Channel products use automatic speed negotiation to interoperate with existing 1Gbit/s Fibre Channel devices.
• 2Gbit/s technology will alleviate congestion, but servers may be unable to support more than one 2Gbit/s host adapter per PCI bus.
• This new generation of Fibre Channel devices will plug and play, moving interoperability problems from the physical layer to the management layer.
• 2Gbit/s should enable Fibre Channel to maintain its lead over iSCSI for some time to come.