Ethernet economics should overwhelm expensive and lower volume Fibre Channel SANs with iSCSI SANs. That's the received wisdom from commentators such as McData's Tom Clark. Linley Group agree and said that after 2007, Fibre Channel will get increasingly choked as Ethernet SANs overtake it.

But according to the Communication Industries Research group, CIR, that's all wrong. It says that Fibre Channel revenue will double to $1.7 billion in 2008, driven by growth in storage area networking.

"While SANs are often associated with disaster recovery and backup," it claims, "rapid data retrieval for financial trading is sustaining much of the market's growth. Additionally, with larger frame sizes, and its Class 1 dedicated point-to-point operation, Fibre Channel is successfully withstanding the challenge from Ethernet in the storage market." And more: "Further stunting the growth of Ethernet for storage applications is a lack of interest in merging LANs and SANs."

The story goes that SANs, particularly ones with more than 5TB of capacity, deliver lots of data to relatively fewer end points. Ethernet is meant for delivering smaller amounts of data to more end points. Its data frames can hold up to 1,518 bytes, whereas Fibre Channel frames can hold 2,048 bytes - 25 percent more. Fibre Channel also has a link path or virtual network set up for point-to-point communications with paths across the SAN set up from the HBA through switch ports to LUNs and disk drives. Not so with Ethernet.

When Ethernet is used for large data flows with TCP/IP the protocol requires acknowledgments to be sent in response to delivered packets. Fibre Channel is better suited, according to CIR, to SAN data traffic flows, and its advantages strengthen as the SAN's stored data increases in size. This situation is what is behind CIR's belief that SAN and LAN convergence is not happening.

Below around 5TB capacity Ethernet appears to have the advantage, according to CIR. It is easier to upgrade a NAS to an Ethernet SAN than Fibre Channel because the existing LAN infrastructure and IT staff knowledge can be used.

Fibre Channel's roadmap from 1Gbit/s to 2Gbit/s to 4Gbit/s to 8Gbit/s with backward compatibility should also enable it to keep ahead as Ethernet heads towards 10Gbit/s and faster speeds in the data centre.

Cost reductions in Fibre Channel port prices will also strengthen the repelling of Ethernet in SANs.