A FCoE Community: Welcome to our community for developers, engineers and resellers interested in FCoE technology innovation.

Part of the market appeal of FCoE is the promise of bridging the SAN and LAN with the reliability of Fibre Channel and the cost economies of Ethernet.  From a protocol development and interoperability perspective, manufacturers of FCoE equipment are on track to deliver fully capable and compliant devices for use in existing storage area networks.  There are still questions, however, as to which cable interconnect technology is most appropriate for use in FCoE-based data centers.

The point of contention is that there are a tremendous number of interconnects within a data center.  A key strategy in keeping price down for FCoE, then, is to use the lowest cost connector and cable that can still get the job done.  Since even a small savings per connector/cable becomes significant when multiplied over so many interconnects, the resulting reduction in overall cost to migrate a SAN to FCoE can be substantial.

Currently, the SFP+ connector is the primary interconnect for FCoE links and supports both optical and copper interfaces.  The optical interface offers the best signal quality and can reach as far as 300 m with multimode type fibre.  Alternatively, the copper SFP+ cable is expected to reach up to 20 m.  Ideally, copper interconnects are preferred because of their lower cost compared to optical interconnects.  These SFP+ copper cables are referred to as “direct attach cable” or DAC for short.  They are also known as “twinax”.  Due to signal integrity issues, passive copper twinax is reported to reach up to 7 m distance only.  Upgrading to active twinax cable improves the reach to 20 m.

In addition, given the dramatic cost advantage and potential reuse of some existing network infrastructure, there are those in the industry who are proposing the use of 10GBASE-T with a standard RJ-45 connector for FCoE links.   The idea of pushing 10GBASE-T for use in the FCoE network infrastructure is driven by the competing iSCSI storage technology. Recently, some industry leaders have announced new 10GBASE-T-based products to support data center applications and, in particular, for 10GbE iSCSI storage applications. With the assistance of enhanced Ethernet, iSCSI has improved the overhead efficiency and becomes a potential candidate for critical SAN applications. Leveraging the low cost as well as long reach of 10GBASE-T connections, iSCSI products potentially gain some positive momentum when competing with FCoE.  I personally think this is the main reason that these FCoE vendors are seriously considering adopting 10GBASE-T technology into their products.

Certainly using 10GBASE-T sounds like a good idea.  However, cost is only one parameter of the FCoE value proposition and, for networks handling mission-critical data, it is not necessarily the most important.  Concerns have been raised about the less reliable data integrity performance of the 10GBASE-T interface compared to twinax cable.  This is important because FCoE technology adopts a similar data processing mechanism and maintains the same level of data integrity, performance, and latency as native Fibre Channel. For FCoE to succeed as a disruptive technology, it must also provide the performance and reliability of Fibre Channel while at the same time reducing system cost.  Cost is certainly an important factor in the successful adoption of FCoE, but such success cannot come if performance and reliability suffer materially as a consequence.

There are other factors beyond equipment cost to account for as well, such as power efficiency.  Consider the following quote from Michael Vizard of Ziff-Davis’ Enterprise Technology Group: “Google engineers have already warned their bosses that the cost of the electricity needed to run the company’s servers will soon be a lot greater than the actual purchase price of the servers.”[1] Since even a small savings per connector/cable becomes significant when multiplied over so many connectors, the resulting power savings between different interconnect technologies can be substantial as well.  As a result, one of the biggest challenges of deploying 10GBASE-T technology will be its still too-high power consumption.

Each of these factors – cost, performance, reliability, and power – need to be balanced when determining which interconnect to use within an FCoE-based data center.  Next time I’ll look at each of these in depth to evaluate the viability of the use of SFP+ copper and 10GBASE-T links.

[1] http://serverdesignsummit.com/English/Conference/Conference_Info.html