Fibre Channel over Ethernet
From Wikipedia, the free encyclopedia
Fibre Channel over Ethernet (FCoE) is a mapping of Fibre Channel frames over lossless Ethernet networks. This allows Fibre Channel to leverage 10 Gigabit Ethernet networks while preserving the Fibre Channel protocol. The specification, supported by a large number of network and storage vendors, was developed by the FC-BB-5 working group of T11. On June 4 2009 T11 approved the FC-BB-5 Draft Standard and forwarded it to INCITS for the publication process as an ANSI standard.
Contents |
[edit] Functionality
FCoE maps Fibre Channel natively over Ethernet while being independent of the Ethernet forwarding scheme. The FCoE protocol specification replaces the FC0 and FC1 layers of the Fibre Channel stack with Ethernet. By retaining the native Fibre Channel constructs, FCoE allows a seamless integration with existing Fibre Channel networks and management software.
Many data centers use Ethernet for TCP/IP networks and Fibre Channel for storage area networks (SANs). With FCoE, Fibre Channel becomes another network protocol running on Ethernet, alongside traditional Internet Protocol (IP) traffic. FCoE operates directly above Ethernet in the network protocol stack, in contrast to iSCSI which runs on top of TCP and IP. As a consequence, FCoE is not routable at the IP layer, and will not work across routed IP networks.
Since classical Ethernet has no flow control, unlike Fibre Channel, FCoE requires enhancements to the Ethernet standard to support a flow control mechanism (this prevents congestion and ensuing frame loss.) The IEEE standards body is working on this in the Data Center Bridging Task Group.
Fibre Channel required three primary extensions to deliver the capabilities of Fibre Channel over Ethernet networks:
- Encapsulation of native Fibre Channel frames into Ethernet Frames
- Extensions to the Ethernet protocol itself to enable an Ethernet fabric in which frames are not routinely lost during periods of congestion.
- Mapping between Fibre Channel N_port IDs (aka FCIDs) and Ethernet MAC addresses
Computers connect to FCoE with Converged Network Adapters (CNAs), which contain both Fibre Channel Host Bus Adapter (HBA) and Ethernet Network Interface Card (NIC) functionality on the same adapter card. CNAs have one or more physical Ethernet ports. FCoE encapsulation can be done in software with a conventional Ethernet network interface card, however FCoE CNAs offload (from the CPU) the low level frame processing and SCSI protocol functions traditionally performed by Fibre Channel host bus adapters.
[edit] Application
The main application of FCoE is in data center storage area networks (SANs). FCoE has particular application in data centers due to the cabling reduction it makes possible, as well as in server virtualization applications, which often require many physical I/O connections per server.
With FCoE, network (IP) and storage (SAN) data traffic can be consolidated using a single network switch. This consolidation can:
- reduce the number of network interface cards required to connect to disparate storage and IP networks
- reduce the number of cables and switches
- reduce power and cooling costs
[edit] Frame Format
FCoE is encapsulated over Ethernet with the use of a dedicated Ethertype, 0x8906. A single 4-bit field (version) satisfies the IEEE sub-type requirements. The other bits in the frame specifically, the source MAC address, destination MAC address, VLAN tags, SOF and EOF are all encoded as specified in RFC 3643. Reserved bits are present to guarantee that the FCoE frame meets the minimum length requirement of Ethernet. Inside the encapsulated Fibre Channel frame, the frame header is retained so as to allow connecting to a storage network by passing on the Fibre Channel frame directly after de-encapsulation.
The FIP (FCoE Initialization Protocol) is an integral part of FCoE. Its main goal is to discover and initialize FCoE capable entities connected to an Ethernet cloud. FIP uses a dedicated Ethertype, 0x8914.
[edit] Timeline
The FCoE standardization activity started in April 2007 is now successfully completed.On Wednesday June 3, 2009, the FC-BB-5working group of T11 completed the development of the draft standard and unanimously approved it as the final standard. The following day the plenary session of T11 approved forwarding the FC-BB-5 standard to INCITS for publication as an ANSI standard.The standard is at:[1]
[edit] See also
- HyperSCSI
- iSCSI
- ATA-over-Ethernet (AoE)
