Converged Network Adapters

Which converged network adapter fits your storage network

Choose a CNA by the storage traffic it has to carry, then by port type, because the controller makers document different storage features for each family.

Storage offload can depend on the exact part number, not only the controller: Broadcom's OCe14000 datasheet sells the same dual-port card as a NIC-only version and as CNA versions, told apart by the suffix on the part number. Check both the controller and the part number against the protocol your SAN uses.

What FCoE needs from the network

FCoE needs a lossless Ethernet network and a Fibre Channel switching function at the far end of the link. Juniper's FCoE documentation states that, to achieve the lossless behavior FC transport requires, the Ethernet network must conform to Data Center Bridging standards, and it describes each server's virtual link as ending at an FC switch or FCF port. Broadcom lists those DCB features in its OCe14000 CNA datasheet: Priority Flow Control (IEEE 802.1Qbb), Enhanced Transmission Selection (IEEE 802.1Qaz) and DCBX, next to FCoE offload to the ANSI T11 FC-BB-5 standard. iSCSI asks less of the switch, because it rides on ordinary TCP/IP.

Partitioning ports with NPAR

NIC partitioning divides one physical port into several partitions, each with its own share of the port's bandwidth. Dell's application note on QLogic's 57800-series adapters lists up to four partitions per port and eight per adapter, transmit bandwidth set per partition, no operating system or BIOS changes, iSCSI and FCoE support, and operation with standard 10GbE switches. Dell's R740 guide offers the same switch-independent partitioning on its network daughter cards.

Choosing a CNA

1. Name the storage protocol: iSCSI, FCoE or both, and check that the part number is a CNA version rather than a NIC-only one.
2. Confirm the switch side: Data Center Bridging and a Fibre Channel forwarder for FCoE, ordinary Ethernet for iSCSI.
3. Pick the port type: SFP+ or SFP28 with optics or direct-attach cables, or 10GBASE-T copper.
4. Match the bracket height, low profile or full height, to the server slot, and decide whether you need port partitioning.

Ports, optics and cables

SFP+, SFP28 and QSFP+ cards need an optical transceiver or a direct-attach copper cable in each port, while 10GBASE-T cards take RJ45 copper cabling. Marvell sells its 8200 Series cards as a -CU version with empty SFP+ cages for copper cables and an -SR version with SR optical transceivers fitted, and the part-number suffix shows which one you are buying. Check the bracket height, low profile or full height, as well. For the switch side, add SFP+ and SFP28 optical transceivers or direct-attach copper cables.

CNA, Ethernet NIC or Fibre Channel HBA

Pick a CNA when one set of Ethernet ports has to carry both network and storage traffic. For Ethernet-only links, browse 10GbE network adapters, 25GbE network adapters or dual-port network adapters, or every server network adapter. A native Fibre Channel SAN takes a Fibre Channel host bus adapter instead. Dell rack servers with an integrated LAN slot use network daughter cards, blade servers use mezzanine adapters, and every card type is under cards and controllers. Upgrading the whole host instead? Start from refurbished Dell PowerEdge servers.

Converged network adapter questions

What is a converged network adapter?

A converged network adapter (CNA) is an Ethernet adapter that carries network traffic and storage traffic over the same ports. Marvell describes its 8200 Series CNAs as running LAN (TCP/IP) and SAN (FCoE and iSCSI) traffic concurrently over one shared 10Gb Ethernet link with full hardware offload, and Broadcom lists iSCSI and FCoE hardware offload for its Emulex OCe14000 CNAs. Storage offload varies by model, so check the controller and part number on each listing.

Do I need a special switch for FCoE?

Yes. FCoE needs Ethernet switches that conform to Data Center Bridging, which Juniper names as the requirement for the lossless behavior Fibre Channel traffic expects, and each server's virtual link has to end at a Fibre Channel switch or FCF port. iSCSI is the exception: it runs over ordinary TCP/IP, so a CNA used only for iSCSI works with standard Ethernet switches.

Is a CNA the same as a NIC with iSCSI offload?

Not quite. Juniper describes a CNA as combining the functions of a Fibre Channel host bus adapter and a lossless Ethernet NIC, so it adds FCoE to iSCSI and ordinary networking. Some cards are sold both ways: Broadcom offers the same dual-port OCe14000 card as a NIC-only version and as CNA versions, told apart by the part-number suffix.