The Many Reasons to Take CNAs Seriously

As convergence and virtualization technologies take hold in even the smallest data centers, few products are as much in demand as converged network adapters (CNA); and for very good reasons. CNAs provide a great way for organizations to cut data center costs and improve performance, while giving them entry into the realm of the new, faster, smarter data center.

A converged network adapter combines the functions of a traditional Fibre Channel HBA (host bust adapter) and a 10Gb Ethernet NIC (network interface card). It supports data networking (TCP/IP) and storage networking traffic on a single I/O adapter using enhanced Ethernet and fibre channel over Ethernet (fCoE). Since data centers have traditionally utilized separate data networks (TCP/IP over Ethernet) and storage networks, clearly one adapter that carries the load of two major tasks is hugely beneficial.

Enhanced Ethernet (a.k.a, data center Ethernet or converged enhanced Ethernet) is an advanced form of the standard protocol that eliminates Ethernet’s inherently “lossy” nature and make 10GbE a viable storage networking transport.

fCoE allows fibre channel to use 10GbE (or higher) while preserving the fibre channel protocol. fCoE supports the same security and encryption protocols as standard fibre channel. CNAs support data center bridging (DCB) over enhanced Ethernet, enabling organizations to deploy a unified data communications fabric for both LAN and storage I/O.

Leading makers of CNAs include Emulex and QLogic. Both make a range of CNAs.

Emulex claims that its CNA products offer the following benefits: 30 percent savings on adapters and switches; 80 percent savings on cables; 40 percent savings on power and cooling; 20 percent increase in virtualization with multiple CPU offloads; improved time to deployment; and simplified management.

Second-gen CNAs

Second-generation universal converged network adapters (UCNAs) provide multiple options to combine network and storage traffic over a 10GbE infrastructure. With UCNAs, high-performance server offloads can be used for fCoE or iSCSI connectivity based on the personality that is loaded to the adapter. The UCNA functionality is nearly transparent to the operating system since it presents both the NIC and the iSCSI or fibre channel functionality.

UCNAs vs. Software Initiators

As in the case of iSCSI software initiators, efforts are under way to develop fCoE software initiators that can work with a standard Ethernet NIC but do not support server offloads. Using CPU resources to process fibre channel or iSCSI traffic has several disadvantages when compared with a UCNA that uses dedicated hardware offload engines for fibre channel or iSCSI protocol processing.

CNAs have generated significant industry interest because they reduce data center total cost of ownership (TCO) while preserving existing data and storage networking investment. A major driver behind the surge towards virtualization is the promise of consolidating individual servers. CNAs aid such consolidation by reducing the number of adapters required for data and storage networking.

Other points worth considering:

  • CNAs connect to servers using the PCI Express expansion interface and improve storage and server performance. CNAs can offload the fCoE protocol processing task, thereby freeing the server CPU resources from doing that task, thereby providing high performance storage connectivity and improved overall CPU utilization. The additional processing power retained by the CPUs provide more CPU bandwidth for enterprise applications and in the case of server virtualization environment, enables deployment of more virtual machines per server.
  • Servers supporting PCI Express (x8 or higher) are capable of utilizing the full potential of dual-port 10Gb/s interfaces of the converged network adapter. By providing the capability to isolate and prioritize different traffic types on the link and by supporting bandwidth guarantees for different traffic types, UCNAs enable efficient consolidation while ensuring that storage traffic is delivered with low latency and without any degradation in performance.
  • Besides reducing the number of adapters required on servers, CNAs cut the amount of cables and switch ports, and the number of PCI Express slots.
  • Enhanced Ethernet makes fCoE more reliable as it eliminates the lossy behavior of Ethernet by using such features as priority flow control, congestion notification, and enhanced transmission selection.
  • CNAs support copper and fiber transceivers with SFP plus form factor.
  • These devices also support many types of cables such as copper twin-ax, copper twisted-pair (Cat 6a), and single-mode and multi-mode fibre.

Herman Mehling has been writing about technology for more than 25 years, and has written hundreds of articles for leading technology publications and websites. He was an editor and reporter at Computer Reseller News, and a PR executive at a number of agencies in the San Francisco area. Mehling has edited three books, including How To Select A Vendor For Web Development (written by Salim Lakhani). Currently, he contributes regularly to:, and Before working in technology, Mehling was the editor of a grocery trade magazine in Dublin, Ireland, and a reporter for a Dublin weekly newspaper. He currently resides outside of Paris.

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