Why 'Unified' Is The Hot New Idea For Data Centers - InformationWeek
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George Crump
George Crump

Why 'Unified' Is The Hot New Idea For Data Centers

It's time to think about running your IP and storage networks together. And Cisco's not the only one that thinks so.

The Problem Today

In the late 1990s, companies built a separate network for shared storage, connecting storage arrays using Fibre Channel. At the same time, the use of IP-based local area networks was expanding for server-to-server and server-to-client communications, voice over IP, and many other services. The result is that today's data center is drowning in its own infrastructure.

The physical problem is in the server itself and the cabling used to connect those servers to the rest of the environment. Typical servers have at least two dual-ported Fibre Channel host bus adapters to connect to storage, and two quad-port network interface cards connecting to the IP network. Those four card slots and 12 cable plugs mean there's little room for expansion, a lot of heat, many wires to track, and a lot of data center space used. From a management standpoint, it requires IT pros to figure out a physical Fibre Channel configuration, set it up, and then try never to touch it once it's working correctly.

The solution, according to vendors led by Cisco and Brocade, is to develop a unified infrastructure based on Converged Enhanced Ethernet or Cisco's Data Center Ethernet, two standards designed to extend the Ethernet specification to storage up to 10-Gb speeds. While Cisco has branded DCE with its own name, the company says it's compatible with CEE.

The goal is to run storage and IP traffic through a unified network interface and a single cable. Even giving servers a second interface and cable path for redundancy, that setup would reduce the cable count from 12 to two, and host bus adapters/network interface cards from at least four to no more than two.

The standards let IT teams do things such as prioritize certain traffic--for example, allocating 60% of the bandwidth to storage. They allow for a pause command for a specific I/O stream; pausing all communication, as is currently done for Ethernet environments, would likely crash an application. DCE includes a multipathing capability that will improve reliability on large networks.

Perhaps the most important fact about these specs--Fibre Channel over Ethernet, or FCoE, and the related CEE and DCE--is that they're not yet ratified by standards bodies. While vendors don't expect dramatic changes, it gives CIOs one more reason to wait, since these standards are the foundational components for unification.

Here's a quick description of a unified architecture. On one end, the Ethernet connects into a converged network adapter, or CNA--available now from Emulex and QLogic, and coming soon from Brocade and others. These CNAs replace the four interfaces required in a server today and translate any of the protocols--Fibre Channel, IP traffic, or FCoE--for the operating system.

At the opposite end of the infrastructure are conventional Fibre Channel-based storage systems. There isn't native FCoE connectivity for storage arrays (though some storage vendors say it's coming), and companies aren't going to rip out existing Fibre Channel storage area networks anyway. So a handover between FCoE and native FC must occur at the middle of the infrastructure.

At this middle point is where there's a divergence in strategies between Cisco and Brocade, the two main infrastructure providers. Cisco envisions a "top-of-the-rack switch" that will predominantly have FCoE ports for making the FCoE connections from the servers. The switch will then have uplink ports to the Fibre Channel SAN switch fabric or the IP infrastructure.

In Brocade's vision, there are three functional block modules in switches like the Brocade 8000. One is a conventional Fibre Channel module to connect to FC-based storage, which also can link a bank of CEE standard-based ports to standard IP ports on standard IP switches, allowing the connection to the corporate local area network. In the early phases of an FCoE infrastructure buildout, companies will need a second switch to extract various protocols and route them to the appropriate switch.

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While these approaches don't sound entirely "unified" to start with, it's important to realize that for most customers unification will be a phased-in strategy starting with consolidation of network interface cards at the servers. It will be quite some time before FCoE interfaces are commonplace at the storage level, so there will be a blended infrastructure for the foreseeable future.

Unified infrastructure doesn't necessarily mean all or nothing with Cisco or Brocade or some other vendor. There's no reason multiple vendors' systems can't co-exist as they do today with Fibre Channel SAN systems. However, as is the case with Fibre Channel, the systems likely will be compatible at "the lowest common denominator," and mixing them is sure to limit the use of some features.

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