Converged network adapters (CNAs) are server hardware adapters which combine the data transfer functionality normally provided by traditional network cards and storage host bus adapters. 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 that used by your LAN traffic.
What are the benefits?
- 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 glass fibres).
- The number of switches is reduced as the two networks (LAN/SAN) converge into a single fabric, hence the nomenclature.
CNAs are typically (but not exclusively) found in large virtual server environments to help reduce infrastructure and management costs.
Fibre Channel supremacy
Still, despite these benefits, native Fibre Channel (FC) still holds some advantages over FCoE. Firstly, native FC is typically already in existence in the datacentre. In order to use CNAs and FCoE, one must replace all the existing (LAN) network hardware with devices that support the datacentre bridging (DCB) enhancements. This is a major infrastructure project in its own right, and the costs should not be underestimated.
Secondly, FC is routable, whereas FCoE (which operates at the IP layer) is not, and there are no plans to make it so. You must use FC-IP to extend or join FCoE SANs over even 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 FC over tens of kilometres.
Lastly, only a few storage vendors have systems with native FCoE interfaces. This will change over time, but if you have legacy FC arrays in your environment which only support FC you’ll need some way of attaching them to the converged network.
Far from dead
The move to a converged network within the datacentre is compelling. However given the constraints above, if your second datacentre is more than 3km away and you need to replicate synchronously between them, native FC connectivity is what you’ll need to implement to achieve your aims. Fibre Channel is far from becoming a dying technology.
Andy Wragg is a senior consultant at GlassHouse Technologies.
Image credit: Flickr (Pascal Charest)