Since the emergence of Fibre Channel SANs in the late 1990s, enterprise IT managers have maintained two sets of networks, one for storage I/O traffic and the other for data network traffic. But system consolidation and SAN expansion efforts are driving the need for a unified fabric where multiple traffic types -- network, storage and clustering -- are all carried over a single network infrastructure.

Several options to unify and extend the reach of storage networks have emerged over the last decade, including iSCSI, FCIP, iFCP and InfiniBand. But these options turned out to be performance intensive, too disruptive or, in the case of InfiniBand, required the introduction of new infrastructure.

To facilitate convergence and overcome the problems encountered with the other attempts, a consortium of storage and data network vendors under the aegis of the INCITS T11 committee is working on a new standard called Fibre Channel over Ethernet (FCoE). FCoE is designed to enable network convergence and cost-effective SAN expansion in the enterprise data center.

The basic concept is to use 10G Ethernet to carry native Fibre Channel traffic alongside standard network traffic. However, Ethernet does not provide the performance and reliability characteristics required for carrying Fibre Channel traffic, so several enhacements are required.

Enhancements to Ethernet

The key drawbacks of Ethernet are that it is prone to high latencies and packet loss when the network gets congested – characteristics that are highly unsuitable for storage traffic. The IEEE is working on enhancements to the Ethernet protocol -- appropriately called Enhanced Ethernet -- that would enable the venerable technology to support multiple traffic types.

Key enhancements to 10G Ethernet include the ability to:

* Control the flow of traffic -- without packet loss -- at a more granular level through the implementation of priority flow control.

* Allocate bandwidth dynamically and ensure QoS for multiple classes of traffic.

* Exchange the new protocol parameters between the end nodes and the switches.

A new family of adapters called converged network adapters (CNA) leverage FCoE and Enhanced Ethernet technologies to enable convergence over the underlying 10G Enhanced Ethernet infrastructure. The FCoE technology maps Fibre Channel traffic directly onto Enhanced Ethernet frames, facilitating Fibre Channel SAN expansion in the enterprise data center without requiring physical extension of the SAN fabric to the additional servers.

The advantages of using the technology to expand SANs include: