FCoE vs iSCSI over Ethernet

Even though FibreChannel over Ethernet (FCoE) gets all the hype, iSCSI over Ethernet is just as capable of converging or unifying data centre servers, storage and networking, proponents say.

The key component in the unified data centre is lossless Ethernet, according to FibreChannel and iSCSI advocates. Yet there is a religious war brewing between the two camps on the best way to integrate storage into an Ethernet-based unified data centre fabric.

"Everybody thinks that if you go against iSCSI or you go against FibreChannel, you're a bigot one way or another," says Craig Chapman, director of Cisco Unified Computing System strategy at systems integrator MCPc in Cleveland, Ohio. "You can't be a protocol passionista. You can't be tied to one way of doing things. It's, 'What's best for the solution based on what you've seen? And you've got to balance those out."

Chapman says iSCSI does not compete with FCoE as a method for unifying a data centre fabric. Both have their place, especially if an enterprise has an installed base of one or the other.

FibreChannel is usually preferred by larger enterprises with a low tolerance for latency and packet loss, and a requirement for high application throughput. But it requires its own infrastructure, which drives up its cost.

Smaller and mid-size enterprises might opt for the less expensive iSCSI, which is more latency tolerant than FibreChannel and "lossy," Chapman says.

"You will see iSCSI in enterprises, especially for replication solutions and for remote office installations," says Steven Scully, research manager for Continuity, Disaster Recovery and Storage Orchestration at IDC. "At the core, those customers will be the big FCoE users. On the other hand, you probably won't find much FCoE in SMB customers."

Since it runs over TCP/IP, iSCSI is susceptible to TCP "overhead," such as the windowing characteristic in TCP, Chapman says. A TCP window is a chunk of data, made up of several packets, sent by a server. After the server receives an acknowledgement from the client that the window has been received -- without errors -- it will send the next window of packets.

If errors occur, the data must be resent. This whole event can introduce latency and packet loss with iSCSI, Chapman says. But nothing precludes a business from converging or unifying servers, storage and networking in a data centre with iSCSI -- indeed, Cisco says its can transport iSCSI over Ethernet just as capably as FibreChannel over Ethernet.

And 10Gbps iSCSI converged network adapters are appearing on the market from Network Interface Card vendors such as Emulex.