Many people still believe iSCSI can't cut it in the enterprise, which is better served by Fibre Channel. iSCSI vendors are doing their best to prove that assumption wrong.
Ever since 10Gbps Ethernet arrived, iSCSI has competed in the numbers game -- especially when stacked against 8Gbps Fibre Channel. But raw throughput isn't everything. To win the debate, Fibre Channel partisans simply look down their noses and observe that no Ethernet-based storage protocol, iSCSI included, can compete with FC's inherent performance advantages.
That conclusion still holds true to a certain extent, but the performance gap separating FC and iSCSI keeps narrowing. Eventually, other factors such as ease-of-use and flexibility may be more important. To decide which tool is right for the job, you need a solid feel for what differentiates FC from iSCSI; simply repeating that FC is "faster," while true, glosses over vital distinctions.
Fibre Channel on top
No amount of fancy new technology will change the fundamental difference between the iSCSI and Fibre Channel protocols: Fibre Channel, regardless of the physical media that it runs on, operates as a layer-two (data link) protocol, while iSCSI operates at the layer-seven (application) level.
Though iSCSI may suffer from some performance disadvantages, it makes up for them with simplicity and flexibility. Unlike traditional Fibre Channel, iSCSI doesn't require its own dedicated network infrastructure; instead, it can share the same Ethernet network that the rest of the data center runs on. And since it runs as TCP/IP, iSCSI traffic can be routed outside of a single broadcast domain -- say, across a WAN to facilitate replication. This can't be done with Fibre Channel without expensive Fibre Channel-to-IP (FCIP) gateways or, occasionally, proprietary vendor-specific solutions that use IP networks.
iSCSI is also very simple to use. While zoning new storage in a Fibre Channel network typically requires a significant amount of knowledge and effort, the same task can be accomplished using iSCSI in far less time and with much of the same skill set that most network administrators already have. To be sure, tuning iSCSI to reach its full performance potential (including such tasks as configuring MPIO) requires extra know-how, but it ends up being easier for most network admins to learn.
Enter Fibre Channel over Ethernet
The advent of Fibre Channel over Ethernet (FCoE) has significantly changed the landscape. FCoE is made possible by new extensions to traditional Ethernet collectively termed "data center bridging" (DCB) or sometimes "converged enhanced Ethernet" (CEE). DCB essentially extends the Ethernet protocol to support the same types of lossless throughput provided by Fibre Channel by implementing similar flow control and prioritization mechanisms.