How NVMe over FC works
The FC Protocol (FCP) allows the mapping of upper-layer transport protocols, such as NVMe, Small Computer System Interface (SCSI) and IBM's proprietary Fibre Connection (Ficon), on top of it to enable the transfer of data and commands between a host computer and a peripheral target storage device or system.
In comparison to SCSI and FICON, NVMe has a streamlined register interface and command set, reduces the input/output (I/O) stack's CPU overhead, lowers latency and improves performance. NVM Express Inc. developed NVMe for use with fast media, including solid-state drives (SSDs) and other memory-based technologies. By contrast, the SCSI command set was designed at a time when slower hard disk drives (HDDs) and tape were the primary storage media, and FICON was created to connect mainframe computer and storage devices.
FC-NVMe simplifies the NVMe command sets into basic FCP instructions. Because Fibre Channel is designed for storage traffic, functionality such as discovery, management and end-to-end qualification of equipment is built into the system.
A major distinction between NVMe-oF, including NVMe over Fibre Channel, and NVMe is the mechanism for transporting commands. NVMe maps requests and responses to shared memory in the host computer via the Peripheral Component Interconnect Express (PCIe) interface protocol. NVMe-oF uses a message-based model to send requests and responses between a host and a target storage device over a network.
NVMe-oF facilitates the use of alternative transports to PCIe to expand the distance over which an NVMe host and an NVMe storage subsystem can communicate. The initial design goal for NVMe-oF was to add no more than 10 microseconds of latency between the NVMe host and NVMe storage target, connected over a suitable network fabric, in comparison to the latency of an NVMe storage device using a local host's PCIe bus.
Large-scale block flash-based storage environments that use Fibre Channel are the most likely to adopt NVMe over FC. FC-NVMe offers the same structure, predictability and reliability characteristics for NVMe-oF that Fibre Channel does for SCSI. Plus, NVMe-oF traffic and traditional SCSI-based traffic can run simultaneously on the same FC fabric.
Infrastructure components that must support NVMe over Fibre Channel to enable the potential benefits include the storage operating system (OS) and network adapter cards. FC storage system vendors must qualify FC-NVMe with their products. Vendors with host bus adapters (HBAs) that support FC-NVMe include Broadcom and Cavium. Broadcom and Cisco are the major FC switch vendors.
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