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Fibre Channel vs FCoE. Fibre Channel rules. For now

By Andy Wragg, GlassHouse Technologies (UK)

Converged network adapters (CNAs) are server hardware adapters that combine data transfer functionality normally provided by traditional network cards with storage host bus adapter (HBA) capability.

CNAs utilise the Fibre Channel over Ethernet (FCoE) protocol to allow storage data to be transferred in an IP packet, using the same physical network as used by LAN traffic.

There are a number of benefits to this approach;

• It allows a single method of cabling to be used throughout the datacentre, thus simplifying the number and type of cables being used.
• Provides a more robust physical medium (copper wires over fibre).
• The number of switches is reduced as the two networks (LAN and SAN) converge onto a single fabric.

CNAs are typically (but not exclusively) found in large virtual server environments to help reduce infrastructure and management costs.

Despite the benefits above, native Fibre Channel still has some benefits over FCoE.

Firstly, native Fibre Channel is typically already installed in the data centre. To use CNAs and FCoE one must replace all the existing (LAN) network hardware with devices that support data center bridging (DCB) infrastructure. This is a major project in its own right, and the costs should not be underestimated.

Secondly, Fibre Channel is routable, whereas FCoE (which operates at the IP layer) is not, and there are no plans to make it so. You must use FCIP to extend or join FCoE SANs, even over short distances.

Thirdly, the maximum distance you can run FCoE over is 3km, although this can be increased using FCIP. Using long-wave transceivers, you can operate Fibre Channel over tens of kilometres.

Lastly, only a few storage suppliers sell systems with native FCoE interfaces. This will change over time, but if you have legacy Fibre Channel arrays in your environment which only support that protocol you’ll need some way of attaching them to the converged network.

The case for moving to a converged network in the datacentre is a compelling one. But, given the constraints listed above, if your second datacentre is more than 3km away and you need to replicate synchronously between them, native Fibre Channel connectivity is what you’ll need to achieve your aims. For now, fibre channel is far from being a dying technology.

Andy Wragg is senior consultant at GlassHouse Technologies (UK).