Interviews

posted on 18 August 2008 19:33

Solution Technology is putting on an FCoE (Fibre Channel over Ethernet) course, so we asked Robert Kembel, the course host, some questions about FCoE and what's happening with it. Here is what he had to say:

Blocks and Files: How do FCOE and iSCSI relate to one another?

Robert Kembel: FCoE is a low-overhead, high-performance encapsulation of Fibre Channel frames for delivery via lossless Ethernet and is primarily focused on data center environments. iSCSI is designed to run over existing networks and relies on TCP/IP to provide acknowledgements, flow control and retransmission, when needed.

While both are designed to deliver SCSI commands over a network, FCoE maintains all of the Fibre Channel protocols and structures to simplify the integration of FCoE and Fibre Channel into a common data center environment. Because iSCSI uses different protocols and data structures integrating iSCSI into a common data center environment requires the use of a gateway to perform the necessary protocol conversions.

Fundamentally, FCoE is Fibre Channel (just with a different physical interface).

Blocks and Files: Will FCoE remove the need for iSCSI?

Robert Kembel: Probably not. iSCSI has the ability to run over existing Ethernets along with company intra-nets for long-distance applications such as remote copy or mirroring. FCoE is based on a lossless Ethernet and will most likely be deployed over a new-generation of products designed for the converged Ethernet environment. These products will support Ethernet enhancements such as Per-Priority Pause flow control, Enhanced Transmission Selection Quality of Service through bandwidth management and traffic prioritization and Congestion Notification and Management.

Blocks and Files: If iSCSI and FCoE co-exist will this encourage the development of converged NICS that have TCP/IP Offload engines for iSCSI and FCoE for FCoE?

Robert Kembel: I think we are already seeing more NICs that provide offloading of various functions. Certainly once you get to 10 gigabits per second, you don't want the system's processor trying to handle low-level link operations along with its normal functions. Whether function is offloaded via dedicated hardware or a dedicated processor or core, this will certainly be the norm at 10 gigabits.

While FCoE does not require a TCP/IP offload engine (TOE), it does benefit from offloading certain Fibre Channel and SCSI protocol functions. With the increasing density of chips, I would expect to see more function offloaded from the system's processor to the adapter.

Blocks and Files: Will FCoE encourage a migration from Fibre Channel SAN networking to Ethernet?

Robert Kembel: I think we will see an evolutionary transition from today's predominantly Fibre Channel SANs to more mixed environments in the future. As companies begin FCoE deployment, FCoE and Fibre Channel will co-exist for some time. If FCoE is as successful as it shows signs of being, I would not be surprised to see the ratio of FCoE links versus native Fibre Channel links swing towards a higher percentage of FCoE link. Most data center environments are fairly conservative so I would expect this to be a gradual transition that follows the normal procurement and replacement cycles.

Blocks and Files: Will FCoE provide an opportunity for Ethernet to become the all-conquering storage networking platform at some point, and be used for both block and file storage access?

Robert Kembel: Many years ago I was at a technology conference and one of the presenters stated that Ethernet would ultimately win out over all other networking technologies such as Fibre Channel and Infiniband. At the time, I thought he was being overly enthusiastic, but if we look at what has been happening with things such as Voice over IP and the transfer of other types of information over Ethernet, it may be that he was more prescient than I gave him credit for at the time.

Blocks and Files: Will the present SAN management superstructure erected on SAN directors from Brocade and Cisco be replicated on Ethernet switches?

Robert Kembel: Given that the FCoE Forwarders are basically Fibre Channel switches with Ethernet ports, the SAN management structure will be present there. I don't expect that enhanced Ethernet switches will adopt the Fibre Channel management structure.

Blocks and Files: Does FCoE give an entry into storage networking for Ethernet switch vendors not currently active in storage networking?

Robert Kembel: The challenges for Ethernet switch vendors will be both technical and operational.

On the technical side, there will be (enhanced) Ethernet switches that snoop the FCoE protocols in order to automatically configure Access Control Lists and Static Forwarding Table entries to provide a more robust storage environment. There will also be FCoE Forwarders that are essentially Fibre Channel switches with one or more Ethernet ports (and may provide one or more native Fibre Channel ports).

The easiest opportunity for existing Ethernet switches will obviously be through enhancements to existing switches to support protocol snooping. Providing the full FCoE Forwarder function requires providing all of the Fibre Channel protocols, functions and services, such as the Name Server, Login Server, Fibre Channel address assignment, Zoning, FSPF, etc. Providing the latter functions essentially involves creating a Fibre Channel switch with Ethernet ports.

On the operational side, most storage solutions are sold as just that - complete solutions. It is very difficult to sell a point product into the data center environment. Getting a new product certified and supported by key storage providers, and accepted by the ultimate customer could present a challenge.

Blocks and Files: Will some kind of virtualised FCoE NIC be produced so that multiple VMS in a virtualised server can have logically separate communications through it?

Robert Kembel: We already have this today for both Ethernet and Fibre Channel adapters and it is reasonable to expect that the same capabilities will exist in Converged Network Adapters for FCoE.

Blocks and Files: How do you rate FCoE products from QLogic, Emulex and NetXen?

Robert Kembel: I think it is still too early to rate FCoE products. The InterNational Committee for Information Technology Standards (INCITS) T11 is still in the process of formalizing the FCoE standard so the current implementations are all essentially "pre-standard".

Existing Fibre Channel providers, such as Cisco, Emulex and Qlogic certainly have a substantial base of Fibre Channel experience to draw upon but may find the Ethernet world new and challenging. For companies with an Ethernet background, they will need to develop a Fibre Channel competency in order to support FCoE. I think that both camps will face some interesting challenges and opportunities as they enter this new converged networking world.

Commentary

So there we are. Steady as she goes. There's not going to be an Ethernet takeover of the data center in the next couple of years and FCoE won't remove the need for iSCSI. That protocol will be used on lossy Ethernets with FCoE being used on lossless Ethernet.

However, over the longer term Ethernet could replace Fibre Channel at which point the need for a storage Ethernet switch providing Fibre Channel fabric-class SAN infrastructure will become apparent in my view. Maybe IBM will develop its SVC to become a networked adjunct to a storage Ethernet switch.

The idea of Ethernet switch vendors having switches that snoop the FCoE protocols is a new one on me and sounds quite strong and realistic. Let's watch out for announcements from Ethernet switch vendors that want to develop product for the FCoE space.

^{[Chris Mellor.]}