What is a Converged Network Adapter (CNA)?

In large enterprise companies, main servers have (at least) two adapters – FC HBA (FIber Channel Host Bus Adapter) & Ethernet NIC (Ethernet Network Interface Card) to connect to the storage network (Fiber Channel) and computer network (Ethernet). Converged Network Adapters  converge the functionality of both the adapters into one. Read on, to find out more…

In the above diagram, both the traditional set up with FC HBA + NIC (and) the new set up with CNA/FCOE are represented. As you can see, with the set up in the first diagram, two separate adapters are required on the server to connect to Ethernet based Computer Network and FC based Storage Network respectively.

But the set up in the second diagram requires just one adapter (Converged Network Adapter – CNA) which carries both Ethernet traffic as well as FCOE traffic in a single cable. This cable connects to one of the Ethernet ports in the Converged Switch that has both Ethernet as well as Fiber Channel ports. This Converged Switch converts the FCOE traffic in to Fiber Channel traffic to be sent to the FC SAN over the Fiber Channel Network. The computer network traffic is directly sent to the LAN over the Ethernet Network.

Salient points about CNA – Converged Network Adapter:

• Fiber Channel Over Ethernet (FCOE) is a standard that encapsulates Fiber Channel (FC) traffic over the Ethernet packets to be run on Ethernet Networks.
• The Converged Network Adapter (CNA) connects to the server using the PCI Express expansion interface.
• CNA can offload the FCOE protocol processing task, thereby freeing the server CPU resources from doing that task.
• The new setup works with Fiber Channel Networks, FC Switches and Fiber Channel Management Utilities. Some vendors even offer converged management utilities for their Fiber Channel products along with the CNA – Converged Network Adapters/ FCOE.
• The main advantage of Converged Network Adapter is the reduction of the number of adapters required on the server, reduction of the amount of cables, reduction in the amount of switch ports, reduction in the number of PCI Express slots (on the server).
• Since most of the Converged Network Adapters support 10 GBEE (10 Gigabit Enhanced Ethernet), the performance of the network carrying both network and storage traffic should be good enough. And since CNA follows the same Ethernet standards, 40 GBEE & 100 GBEE will be supported in future.
• There are special switches that support FCOE capabilities on their Ethernet ports. They either come as stand alone switches with both Ethernet/FCOE Ports & FC Ports (or) Chassis based switches that support both Ethernet/FCOE & FC Blade modules.
• Some vendors offer these FCOE supported Switches as Ethernet only (with a lower price), to connect to the computer network presently.  But, FCOE & FC functionalities can be included in the future (through a software upgrade), whenever required.
• Converged Enhanced Ethernet Standard for Data Center Networks is recommended for carrying FCOE traffic, but is not mandatory. So, FCOE based switches can work with normal Ethernet based switches as well.
• CEE – Converged Enhanced Ethernet makes FCOE Storage Network more reliable as it eliminates the lossy behavior of Ethernet by introducing some features like Priority flow control, Congestion Notification, Enhanced Transmission Selection, DCB Capability Exchange protocol, etc.
• CNA supports Copper and Fiber Transceivers with SFP Plus Form Factor.
• Many types of cables like Copper Twin-ax, Copper Twisted Pair (Cat 6a), Single Mode & Multi Mode Fiber are supported by CNA/FCOE.
• Sever Virtualization Vendors support Converged Network Adapters for further reduction in the required hardware for Data Centers.
• Converged Network Adapters can be used as stand-alone 10 GE NIC (Network Interface Cards), if storage networking is not immediately required. FCOE & FC SAN functionalities can be added later on.

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