Interviews

posted on 29 July 2008 08:44

With a couple of Ethernet market trends going on simultaneously how are the roles of Converged Network Adaptors (CNAS) and TCP/IP Offload Engine (TOE) cards developing?

Ethernet is transitioning to 10 gigabit/sec I/O speed (10GbE) for high-bandwidth applications in the data center as the amount of data to be carried by the data center LAN increases. There are two storage applications here. One is for iSCSI with an Ethernet Network Interface Card (NIC) carrying iSCSI packets, that is SCSI commands wrapped up inside TCP/IP packets and sent to an iSCSI target such as a drive array. Typically a host server would convert the SCSI commands and data into TCP/IP packets and use a lot of processing cycles in the task.

TCP/IP offload cards emerged, TOEs, to do this work along with functioning as a NIC. Alacritech is a vendor and developer of such cards.

The second storage application is FCoE (Fibre Channel over Ethernet) in which Fibre Channel block storage traffic and Ethernet LAN traffic are converged onto 10GbE with the Fibre Channel protocol being carried over Ethernet (FCoE) and entering the network via a Converged Network Adapter (CNA) which merges the functions of a Fibre Channel Host Bus Adapter (HBA), roughtly equivalent to a NIC but for Fibre Channel, and a standard NIC.

We discussed the inter-relationship of CNAs and TOEs in the light of 10GbE with Alacritech's director of marketing, Doug Rainbolt. The discussion was sparked off by news that Alacritech has 10Gbe cards being evaluated  by major OEMS.

B&F: How do 10GbE cards relate to converged network adapters from QLogic and Emulex?

Doug Rainbolt: First of all, it's great that the world is converging around 10G Ethernet. When QLogic and Emulex address converged Network Adapters, the convergence incorporates SAN, HPC, and LAN traffic. It all sits on top of 10GbE. We too believe in the idea of convergence, but our strategy relative to storage is a bit different. Alacritech's 10GbE implementation assumes that the storage transport makes use of TCP and the standard Microsoft iSCSI initiator. While TCP has been accused of being CPU-intensive, it does have the long-proven ability of reliable delivery, both for the local and wide area.

With Dynamic TOE enabled, the CPUs on a server are freed up, so the CPU bottleneck is largely removed. QLogic and Emulex have opted to support FCoE, versus iSCSI. Their model assumes that the primary storage model is still resting on Fibre Channel protocol running over Ethernet. It is not taking advantage of TCP. It in essence becomes an iSCSI versus FCoE argument. Customers that have made significant investments in Fibre Channel, including staff, may be attracted to FCoE. Customers looking to move to networked storage, who are quite comfortable with TCP and Ethernet, will opt for iSCSI. Note that QLogic does market iSCSI HBAs, but this is a different product (not a converged adapter).

B&F: Is the Data Center class Ethernet (DCE or Converged Extended Ethernet) market a separate one from that of accessing an iSCSI SAN over Ethernet?

Doug Rainbolt: Yes. While the FCoE vendors may say that they will look for ways to handle the "occasional" TCP traffic; their underlying belief is that the primary storage model will be FCoE.

Again, iSCSI takes full advantage of TCP, FCoE does not. As a consequence, the vendors have to make enhancements to Ethernet infrastructure to enable lossy behavior. Not trivial. Flow control and congestion management become concerns. Our position is why not just use TCP and Dynamic TOE? The FCoE vendors will suggest that iSCSI plays in the SMB while DCE and FCoE are for the enterprise. While iSCSI certainly appeals to the SMB, many large enterprises like it.

B&F: How will Acritech's 10GbE cards be positioned for use in virtualized servers running VMware, Hyper-V, Virtual Iron or Citrix XENserver?

Doug Rainbolt: First, you should expect Dynamic Offload (Such as the Chimney model) to have full support for virtualized environments in the future. This requires cooperation from the O/S or Virtualization vendor. In the interim, as Alacritech adapters can function as both a Dynamic TCP Offload adapter and NIC, there are standard virtualization features that could be provided under "NIC mode". Stay tuned.

B&F: Does Alacritech have a blade server form factor for its cards, including the 10GbE cards?

Doug Rainbolt: Good question. The OEMs in the Blade server market, typically invite the card manufacturers to design mezzanine versions of their technology. There are no guarantees that you will get any business. Unfortunately, there is no standard design that would accommodate all of the OEMs. If there were, we'd be all over it. We have been asked repeatedly to join the club, pay the dues in designing such a card, and work with the OEMs channel partners and see what happens.

Our strategy is really to focus on rack and tower servers as there is still very large market opportunity there. If we do our job right, we believe that the OEMs will come back to us, putting a bit more "firmness" and predictability into the opportunity. Being a small company, this is what we have to do. We're placing our bets very carefully.

Commentary
The FCOE convergence story is not a story about the convergence onto a single network method for all block storage access. There are two methods; Fibre Channel and iSCSI. As iSCSI target arrays become more powerful and capable, witness developments from, for example, LeftHand Networks, Dell EqualLogic and NetApp's iSCSI arrays, then we can expect the iSCSI arrays to need 10GbE TOEs to provide the storage bandwidth needed for servers and virtualized servers to access their block storage resources.

FCoE is the other block storage access protocol and it's conceivable, quite conceivable, that in large shops we may well see a 10GbE network carrying both iSCSI and FCoE traffic.

There seems little prospect of FCoE walking all over iSCSI or the reverse so we should expect a 2-horse block storage access race to continue for the forseeable future.

^{[Chris Mellor.]}