Fibre Channel and Fibre Channel over Ethernet
If you are new to data center technologies, you may be hearing the term Fibre Channel for the first time. Fibre Channel is described as a networking technology that achieves rapid transfer rates. Fibre Channel can be configured at the speeds of 2, 4, 8 and 16 gigabits per second. Fibre Channel has origins in the supercomputing world. These days, Fibre Channel is typically used within enterprise data centers. More specifically, SAN storage commonly utilizes Fibre Channel as a connection medium. Fibre Channel achieves connectivity using fiber optic cabling however some setups utilize an electrical interface.
Fibre Channel over Ethernet is commonly referred to as FCoE. When 10 gigabit Ethernet based networks are in place, the Fibre Channel protocol can be run over Ethernet. At first glance, it seems as if you could use this medium to directly connect to your storage. There is a method to do this and it requires a converged network adapter. Keep in mind that FCoE is unable to directly route to the IP layer of your networking stack. FCoE can be used to interconnect storage devices that are already connected using Fibre Channel as a means of connectivity. Using FCoE to introduce additional SANs into your pool allows you to add Fibre Channel based resources without having any downtime. Using FCoE also allows you to reduce the amount of cabling needed in order to install your storage solution.
When connecting SANs using FCoE, an FCoE switch is needed. The FCoE switch facilitates the traffic between the LAN, the SANs and the converged network adapter. The converged network adapter allows data center administrators to reduce cabling due to the fact that the Ethernet’s NIC card and Fibre Channel host bus adapter are all on the same board within the CNA. When you compare a traditional Ethernet based storage network versus a Fibre Channel over Ethernet based network, you can begin to see why more administrators choose the FCoE model; as the FCoE model reduces cooling costs, reduces the total amount of infrastructure needed for the project while providing a streamlined approach to SAN storage connectivity.
What About Packet Loss?
A natural concern of FCoE would be packet loss. Remember, since FCoE does not hold TCP information, the SCSI layer would be responsible for recovering the packets. This type of setup would be unrealistic for most enterprise environments. That’s why FCoE must work in a lossless nature. This has largely been solved by converged network adapter vendors. FCoE must be configured in a manner that gives storage packets the highest priority and those packets should be routed accordingly. Administrators can assign traffic with lower priority to routes that could lose packets. FCoE can be setup in a redundant fashion with multiple uplinks which ensure the lossless nature of data transmission within SANs.
