The buzz about Fibre Channel over Token Ring has built rapidly over the last week. Industry experts like Greg Ferro, Denton Gentry, and Joe Onisick have weighed in (as have I), and the Packet Pushers Podcast featured the news in show 12, “Get on the Ring!” Some have called out FCoTR as a foolish hoax, but the FCoTR phenomenon is not foolish. Indeed, FCoTR gives everyone in the industry the chance to reevaluate the current state of the art and has exposed real weaknesses in the Ethernet-centric future of the data center.
The Best Tech Rarely Wins
It has become something of a maxim in technology circles that “the best technology rarely wins.” While many point to the victory of VHS over Betamax, techies often look to the success of CISC over RISC, Windows over UNIX or OS/2, and PC over Macintosh. In every case, it was the plentiful availability of cheap “good enough” products that trumped any apparent technical superiority. And in every case research and development led the purported “inferior” technology to eventually surpass the capabilities of the favorite.
The market failure of Token Ring was an ideal case study for what might be called the Betamax lesson. The token-passing scheme served to enhance both reliability and predictability. Unlike Ethernet, which focused on fault tolerance with “conversational” CSMA/CD, Token Ring took an ordered “Roberts Rules” approach with each station waiting for permission before transmitting. This mechanism could also allow a station to reserve bandwidth for a critical application. Token Ring networks were inherently faster than Ethernet as well, at 4 Mb/s, 16 Mb/s, and eventually 100 Mb/s. But the expense and complexity of cabling caused it to lose favor. This was especially true once 100BASE-TX Ethernet became common: It was fast enough for most LANs and wide support and availability made it incredibly cheap. Gigabit Token Ring was standardized in 2001 but never implemented.
The Elephant in the Room
Ethernet has developed rapidly since it became the de facto data center standard. Gigabit Ethernet ports and switches are common today, and engineering has made it fairly reliable and interoperable in practice. The spread of IP networks also helped Ethernet: Many applications rely on TCP for reliable communication, masking collisions and data link errors even as CSMA/CA and improved DSPs reduced their frequency. The industry is currently shifting again, with 10 GbE becoming more common and 40 Gb and 100 Gb Ethernet standardized and rolling out in high-end switches. Convergence is the word of the day in data center circles, and Ethernet is the heir apparent to rule the converged world. To handle new traffic types (Fibre Channel and RDMA, for example), Ethernet is being extended with prioritization and reservation of bandwidth, advanced congestion management to avoid packet loss, and a mechanism to specify what capabilities are present.
From Star Trek III:
James T. Kirk: Scotty, as good as your word
Montgomery Scott: Aye, sir. The more they overthink the plumbing, the easier it is to stop up the drain. Here, Doctor, souvenirs from one surgeon to another. I took them out of her main transwarp computer drive.
Although interest (and much enthusiasm) in these Data center bridging extensions is widespread, an undercurrent of trepidation is present as well. Storagers worry whether Ethernet is really ready to handle their precious cargo, and networkers are concerned over the proprietary and complex nature of these add-ons. Independent voices also fear the gusto with which vendors are endorsing them, with Fibre Channel over Ethernet (FCoE) becoming a particular object of skepticism. Many see these moves as a land grab rather than a use case-driven expansion.
We may laugh at the idea of Fibre Channel over Token Ring (FCoTR) in today’s data center, but the concept also exposes real fears about a future data center dominated by converged I/O reliant on Ethernet. The putative features of FCoTR are exactly the weaknesses traditionally seen in Ethernet: Packet loss, congestion, and mediocre hardware make it unsuitable for sensitive payloads like storage. Would a resurgence of Token Ring, engineered with these in mind, really be so bad?
Although data center extensions and “big iron” equipment promise to eliminate these weaknesses, many remain concerned about an Ethernet-dominated data center. At what cost will these enhancements be delivered? Do we really need them? There is also a real technical concern that Ethernet might not withstand another round of bracing and might instead fall over on its crutches. At the very least, data center-class Ethernet is late and overweight. It is wise always to carefully consider which step to take next when so much is on the line.