FCoE leverages Fibre Channel's use of SCSI directly over Ethernet, in contrast to iSCSI which uses a different encapsulation method to send SCSI over TCP/IP, which then usually goes over Ethernet. By running directly on Ethernet, it sidesteps the TCP/IP transport and network protocols that introduce latency, making it more suitable for high-end storage applications.
Unlike iSCSI, existing storage resource management applications for Fibre Channel SAN environments will still work with FCoE. This ability to blend seamlessly with existing Fibre Channel networks, providing compatibility with existing storage, drivers, and management tools, is a big plus.
The growing demand on datacentre resources, such as the recent boom in virtualisation which places pressure on users' I/O links, and in turn drives demand for 10Gbps Ethernet makes network convergence an attractive prospect. A unified fabric, in which server and storage networks converge on shared links – will slash the number of adapters and cables needed, removing tens of watts of power from every server. This lowers both capital and operational costs and eliminates cabling headaches in crowded datacentres. However, when large volumes of storage traffic are being carried, the shared cabling and convergence benefits of using FCoE pipes may not be realised, as there would be no excess capacity to carry any other type of traffic.
Although it is technically possible to run FCoE on standard Ethernet, it would not be sensible to do so, because standard Ethernet tends to introduce latencies beyond those of TCP/IP, by dropping and then having to resend data packets. The IEEE is currently developing a standard for a lossless version of Ethernet usually referred to as Data Centre Ethernet (DCE) or Converged Enhanced Ethernet, on which FCoE will be most likely be carried.
While FCoE's independence from TCP/IP makes it suitable for networking within the data centre, it makes it much less suitable for wide-area networking. This means it will not replace FCIP (Fibre Channel over IP), which was created specifically for use in wide-area links between storage networks, nor iSCSI, which can also be used for wide-area storage networking. Elsewhere, iSCSI will still be the local storage network of choice wherever customers need to run low-cost storage networks without datacentre performance.
In summary, FCoE is a good fit for servers that can benefit from the convergence of networking traffic - server clustering, messaging and storage traffic - onto a 10Gbps Ethernet common interface in order to reduce networking costs.
This was first published in March 2008