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#FCoE #SAN multi-hop technology primer

May 11, 2011

Read the full SearchStorage Article @ …FCoE SAN multi-hop technology primer.

What you will learn in this tip: Fibre Channel over Ethernet (FCoE) storage-area network (SAN) technology is becoming more popular in data storage environments, but there are performance issues, primarily the lack of multi-hop switching support, that need to be addressed that could potentially stunt the growth of the technology. Find out what vendors and users are doing to improve FCoE SAN performance.

FCoE SAN is gaining broad support from storage and network vendors, and customer adoption is also rising. Because it’s a new protocol and relies on many new features, FCoE remains somewhat limited in terms of interoperability and flexibility. One often-criticized element is the lack of multi-hop switching support in FCoE SANs, but what exactly does this mean?

A quick Fibre Channel primer

Fibre Channel (FC) initiators contain a number of Node Ports (“N_Port”) that connect to the Fabric Ports (“F_Port”) on switches. FC switches talk to each other using Expansion Ports (“E_Port”) before finally communicating with the N_Port on the storage array. This allows them to route traffic through the SAN to avoid data loss and congestion. FCoE SANs adopt a virtual version of this configuration, with a “VN_Port” talking to a “VF_Port,” and (if they support it) the network switches using “VE_Ports” to exchange data over an inter-switch link (ISL).

One major difference between a Fibre Channel fabric and Ethernet network is intelligence: The fabric itself actively participates in access and routing decisions. Although it’s distributed, the FC fabric has some intelligence and thus FC switches are more involved in the network than basic Ethernet switches. In particular, each switch participates in making decisions about where to send data traffic, so each stream of initiator-to-target traffic gets its own route through the SAN rather than sharing a single route as in an Ethernet LAN with spanning tree path management.

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