Fibre Channel vs. iSCSI: The war continues

FCoE (Fibre Channel over Ethernet) is the newest storage networking protocol of the bunch. Ratified as a standard in June of last year, FCoE is the Fibre Channel community's answer to the benefits of iSCSI. Like iSCSI, FCoE uses standard multipurpose Ethernet networks to connect servers with storage. Unlike iSCSI, it does not run over TCP/IP - it is its own Ethernet protocol occupying a space next to IP in the OSI model.

This differential is important to understand as it has both good and bad results. The good is that, even though FCoE runs over the same general-purpose switches that iSCSI does, it experiences significantly lower end-to-end latency due to the fact that the TCP/IP header doesn't need to be created and interpreted. The bad is that it cannot be routed over a TCP/IP WAN. Like FC, FCoE can only run over a local network and requires a bridge to connect to a remote fabric.

On the server side, most FCoE implementations make use of 10Gbps Ethernet FCoE CNAs (Converged Network Adapters), which can both act as network adapters and FCoE HBAs - offloading the work of talking to storage similar to the way that FC HBAs do. This is an important point as the requirement for a separate FC HBA was often a good reason to avoid FC altogether. As time goes on, servers may commonly ship with FCoE-capable CNAs built in, essentially removing this as a cost factor entirely.

FCoE's primary benefits can be realized when it is implemented as an extension of a pre-existing Fiber Channel network. Despite having a different physical transport mechanism, which requires a few extra steps to implement, FCoE can use the same management tools as FC, and much of the experience gained in operating an FC fabric can be applied to its configuration and maintenance.

Putting it all together

There's no doubt that the debate between FC and iSCSI will continue to rage. Both architectures are great for certain tasks. However, saying that FC is good for enterprise while iSCSI is good for SMB is no longer an acceptable answer. The availability of FCoE goes a long way toward eating into iSCSI's cost and convergence argument while the increasing prevalence of 10Gbps Ethernet and increasing server CPU performance eats into FC's performance argument.

Whatever technology you decide to implement for your organisation, try not to get sucked into the religious war and do your homework before you buy. You may be surprised by what you find.