Fibre Channel is the choice for resilient storage networks due to its reliability and robust set of management capabilities. Mainframe computers that run the world’s financial systems, high speed transactions processing, fraud protection, and reservation systems rely on Fibre Channel because it provides performance and reliability these systems demand for 24/7 availability.

Mainframe systems use FICON and High Performance FICON protocol to carry Single Byte commands (SBCCS) over Fibre Channel to communicate with storage. FICON and High performance FICON are defined in the T11 Fibre Channel standards as FC-SB-6 Command Mode and Transport mode, respectively. FC-SB-6 (FICON’s 6th generation) is an FC-4 Upper Layer Protocol (ULP) that runs on top of the Fibre Channel FC-2 layer (defined by FC-FS-4) just like the FCP protocol (T10’s FCP-4) is used to carry SCSI commands over Fibre Channel.

It’s a common misconception that FCP is Fibre Channel and Fibre Channel is FCP and it is all about SCSI commands. FCP is merely an FC-4 layer command and data transport protocol that was initially defined to carry SCSI commands over Fibre Channel Layer 2. However, realizing that the FCP-4 transport provides the lowest overhead and streamlined operations, High
Performance FICON uses the same FCP-4 transport for commands and data as SCSI FCP does.

In fact, the new NVMe over Fibre Channel Fabrics standard (FC-NVMe) also chose to make use of the FCP transport for commands and data because it provides for the lowest latency to carry NVMe operations over Fibre Channel. The steps of an FCP operation very much parallel the steps of an RDMA operation, which is touted in the technologies outside of Fibre Channel as a necessary component for low latency I/O. Figure 1 shows the sequences of an FCP Read

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