FCoE - or iSCSI?

Fibre Channel over Ethernet, a new protocol, was announced recently. How does it relate to iSCSI? FCoE means using Fibre Channel protocol over Ethernet. whereas iSCSI means using TCP/IP protocol over Ethernet. The former gets you to a Fibre Channel SAN across an Ethernet link, the latter to an IP SAN. But iSCSI is being presented by many suppliers as a Fibre Channel SAN extension product. So if both iSCSI and FCoE can get you to a Fibre Channel SAN over Ethernet, which should you use?

Emulex' Taufik Ma, intelligent networking products VP, said: "iSCSI provides block storage over Ethernet using a unique protocol to carry SCSI commands, and a relatively expensive TCP/IP transport. This requires an iSCSI infrastructure to be managed differently, using different tools than the existing SAN management tools enterprise data centres use today. FCoE consolidates fabrics, simplifying the overall data centre infrastructure, while ensuring leverage of existing FC SANs."

He also said: "iSCSI is complementary to Fibre Channel, serving different market needs. iSCSI addresses standard servers outside the data centre, and provides SAN technology for those that don't have a significant Fibre Channel infrastructure. FCoE is designed to provide unified wire support within the data centre. The Ethernet enhancements will benefit iSCSI deployments along with Fibre Channel over Ethernet deployments."

In other words, iSCSI isn't to be used for FC SAN extension; that role falls to FCoE.

FCoE standards efforts

FCoE would enable SAN traffic to be natively transported over Ethernet networks, while protecting and extending the investment that customers have made in FC storage networks. The proposal for a new direct mapping of Fibre Channel over Ethernet has the support of industry leading vendors including, Brocade, Cisco, EMC, Emulex, IBM, Intel, Nuova, QLogic, and Sun Microsystems. This group has proposed the creation of a new FCoE technology specification to the T11 Committee of the American National Standards Institute (ANSI).

FC answer to iSCSI

Presumably this group does not want to see iSCSI eat into FC revenues and cramp FC's expansion. The members say FCOE provides seamless extension and protection of existing - FC - investments. It would give customers a unified data centre fabric that meets the reliability, latency, and performance requirements for storage and broader data centre connectivity. Also additional server connectivity options for more cost-effective data centre networking .

That's the key. Okay, yes, FC HBAs and FC cable were expensive if you wanted to hook second line servers up to the FC SAN. So, yes, iSCSI did look interesting because you could use well, known, well-understood and cheap Ethernet and IP to get the FC SAN. But that gives you parallel storage networking structures and complicates things. Better to have a unified FC fabric and carry its protocol over Ethernet to hook up secondary servers without needing HBAs or other FC kit, or IP as well.

It's ironic really. This bunch of people is saying that, because of the installed FC base its cheaper to carry FC over Ethernet than have an all-Ethernet set-up. Ethernet economics only partially rule, okay?

EMC's Chuck Hollis, a technical alliances VP, was pleased about FCoE. It's a great idea to base FC SAN extension on Ethernet economics - cheap NICS vs expensive FC HBAs - without having to stop using Fibre Channel.

In his blog he notes: "... the industry's first try -- iSCSI -- only achieved partial success. The good news is that everyone ended up supporting it (including a few OS heavyweights like Microsoft who actually drove adoption). And iSCSI has found a nice market home in new, smaller SANs where no FC is present. Yet, at the same time, compared to the aggregate storage market, it's still a very small fragment. Proponents pointed to fast iSCSI growth rates, but -- according to IDC -- that's slowed as well. And if you work in large enterprises that have made investments in FC infrastructure, you've probably noticed that they're just not interested in talking about iSCSI -- period."

For him iSCSI has no role in enterprise storage networking. FCoE should or might have because:-

- A direct one-to-one mapping of FC frame to Ethernet frame. No IP protocols. No extra stuff. As close to a bare-metal protocol as you're likely to see. This means fast and simple.
- Mechanisms (as part of the proposed standard) to guarantee latency without retry. FC does that, FCoE mimics this behavior.

"At its simplest level, it's a straightforward attempt to bring the economics of Ethernet hardware (in this case 10gE) to the enormous world of FC SANs by not trying to do too much."

For Hollis, iSCSI has its role to play but it isn't in the corporate data centre.