For enterprises that have already deployed Fibre Channel SANs, the question of the moment is not whether iSCSI or Fibre Channel is the superior technology. Rather, the real dilemma is trying to get the two protocols to work together as a seamless storage environment.
There are many good reasons to launch iSCSI in a Fibre Channel environment, cost and flexibility among them. But there are a number of considerations to take in when planning an integrated environment, according to blogger Steve Bigelow. Among them is the fact that FC does not always outperform iSCSI, particularly with applications that don't require a lot of bandwidth -- and if you have the foresight to deploy specialized iSCSI NICs using TOE (TCP/IP Offload Engine) technology.
iSCSI/Fibre Channel integration is also being helped along by the Fibre Channel over Ethernet (FCoE) standard backed by Brocade, Cisco, Emulex, QLogic and others. One of the chief advantages here is that FCoE maps the SCSI protocol directly to the Ethernet -- something not even iSCSI can do -- which means you can still use your existing Fibre Channel management applications to manage your SAN.
The biggest drawback to FCoE, however, is the fact that it is not routable, due to the absence of a TCP/IP component. That means it's largely restricted to the LAN. For wider use, you'll need a Fibre Channel over IP device, currently under development at Brocade and Cisco.
What's most interesting about FCoE is that many pundits have long been predicting the end of Fibre Channel in the face of low-cost competition from iSCSI. But now that an all-Ethernet SAN is within the realm of possibility, it could be iSCSI that has a tough time competing on a level playing field. In the meantime, however, there are still plenty of environments that land themselves to a mixture of both.