Green data center networks: Smarter architecture, not expensive devices

When it comes to green data center design, most think of server and storage consolidation. But green networks, with improved port utilization, play an important role without requiring investment in expensive new devices.

When IT teams look to slash electricity consumption in the data center, network devices don't escape the spotlight. After all, these devices have been increasing in size and complexity for years, and a large core switch or router consumes a fair amount of power.

But should investing in green-certified devices be your first move toward network efficiency? Not necessarily. There are many steps you can take now and in the long term to ensure that your network doesn't cost you more than it should in electricity or in overall environmental impact.

Data center energy efficiency: The network's not the culprit

The first step should be to squeeze as much energy saving as possible out of servers and storage systems, which are the biggest drains. The network is actually a minor player in terms of electricity usage in the data center. Most models attribute anywhere from 10% to 15% of overall data center electricity consumption to network devices.

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Keeping it green: Design principles for efficient network architectures

Consolidating servers and storage for maximized usage will result in enormous energy savings almost immediately. Just a few years ago, the average utilization of servers in most companies was less than 10%. In storage systems, utilization is at about 50%. With numbers like that, most companies are able to consolidate servers and storage for a 30% reduction in power utilization.

Green data center networks: Consolidated devices and increased port utilization

While a network device can be designed to be more or less efficient, the difference will not be sufficient to justify a "forklift" network upgrade. The key to greening networks is to look at architecture in the short term and layer-1 (media) strategy for the longer term.

In the short term, your network architecture will determine overall power consumption more than any single device. Overall power consumption is mostly determined by the number of network devices switched on. And that number depends on network design, architecture and utilization.

A network switch that has only a few of its ports connected still consumes a lot of power to run the backplane and switching logic. The problem of underutilized switches is amplified by the hierarchical architecture of the network. Each underutilized access layer switch is also connected upstream to at least two distribution switches. In most switched networks, the infamous spanning-tree protocol ensures that there are no loops by switching off redundant links. It's a cascade effect: An underutilized access switch is connected through 50% "off" uplink ports to two underutilized distribution switches. The three-tier switching architecture is meant to allow for rapid growth and scalability at the access layer, but it also amplifies the problem of low utilization.

In the short to medium term, therefore, you can green your network by consolidating switches and increasing port utilization. From an architectural perspective, a greener network is a flatter network, with greater utilization and less "sprawl." Fortunately, this trend coincides with the overall industry trends that are driven by virtualization and consolidation in servers and storage.

Nix the distribution layer?

Many of the companies participating in Nemertes' research are going as far as removing the distribution layer from their network architecture. Larger core switches can, in most cases, support the bandwidth and port density (using 10 gigabit Ethernet) for a very large access layer (many thousands of 1 gigabit access ports). Depending on the initial utilization, network consolidation can reduce ports and therefore power use between 5% and 30% on most networks.

Green networking for the branch office

Beyond the data center, much of your network is probably in branch offices. Nemertes' research shows that in 2009, 89% of employees are working away from headquarters, leading to an explosion in the number of branch, regional and remote offices. In the branch office, the way to green the network is once again through reducing the number of network devices.

For the most part, that means replacing a stack of independent network appliances with a single multi-purpose appliance that offers connectivity, optimization and security functions. The power savings can be quite dramatic, especially since you will most likely replace aging devices with more power-efficient, modern designs.

Most vendors offer multi-function branch appliances either as optimization devices with added security or as security devices (labeled unified threat management) with added optimization features. Consolidating branch devices can lead to dramatic power savings. Replacing four aging devices with one multifunction device, for example, will give you greater than a 75% reduction in power.

Cabling still matters: Optical fiber for data center efficiency

The final consideration for a green network is a long-term strategy for your cabling infrastructure. The battle between copper and optical fiber cables has been waged for years, but copper is increasingly falling behind. From an environmental perspective, copper cabling has two major disadvantages. First, it is built from a nonrenewable, increasingly rare and expensive metal. Second, it takes more and more power to push electrons through copper at the speeds we demand, leading to massive per-port power consumption compared with optical interfaces. For both of those reasons, you should be planning to migrate much of your network to optical fiber within the next decade.

Is green networking worth the time and trouble?

Improving network utilization won't produce the same kind of results as server consolidation. Even if you were to achieve a 30% increase in power efficiency in the network (a very tall order), you would save only 3% of overall data center electricity and emissions. Still, green networking can't be overlooked in the equation.

Although you will not get as big an impact from greening the network as you will with green servers or green storage, most of the changes you will make are consistent with the broader industry trends: consolidation of network devices, flatter network architecture, and implementing optical fiber infrastructure. Keep these decisions in mind as you plan your network upgrades, and the road to a green network will be smooth and straight. It turns out that going green can be about a lot more than buying devices that are certified green. The sustainability mantra, "reduce, reuse, recycle," always starts with "reduce."

About the author

Andreas M. Antonopoulos is a senior vice president and founding partner with Nemertes Research, where he develops and manages research projects, conducts strategic seminars and advises key clients. Andreas is a computer scientist, a master of data communications and distributed systems, a Certified Information Systems Security Professional (CISSP) and a self-professed geek, with an engineering, programming and consulting background.


This was first published in August 2009

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