Capacity Planning: Art, Science or Magic?

Science fiction writer Arthur C. Clarke told us that ”Any sufficiently advanced technology is indistinguishable from magic.” Anyone who has worked in IT for long can tell of the miracles they have pulled off. But a manager’s job description doesn’t stop with technical wizardry. It also includes that other piece of the black arts: predicting […]

Written By
Drew Robb
Drew Robb
Published: Aug 27, 2004
Updated: Jan 28, 2021
6 minute read
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Science fiction writer Arthur C. Clarke told us that ”Any sufficiently advanced technology is indistinguishable from magic.”

Anyone who has worked in IT for long can tell of the miracles they have pulled off. But a manager’s job description doesn’t stop with technical wizardry. It also includes that other piece of the black arts: predicting the future.

No, not something as simple as who will win next spring’s Oscars, but how many bits users will send over the network in six months, or how many terabytes of storage they will consume.

”Capacity Planning as an art form has become more important since the dot.com meltdown, as it demonstrated the dangers of building networks to dubious over-rated forecasts or philosophical visions,” says Andy Bolton, Chief Executive Officer of Capacitas, Ltd., a capacity planning consultancy with offices in London and New York. ”Networks should only be built to customer demand, which is difficult but achievable.”

How exactly, though, do you achieve it?

Crystal balls and tea leaves are notoriously inaccurate for predicting IT utilization. One needs the magic of capacity planning tools.

Following the Trendsetters

The simplest form of capacity planning is trending — taking past and current utilization figures, and using these to estimate future growth trends.

”Trending does enable reasonably accurate quick-and-dirty analyses to take place, with a good return on investment for this work,” says Bolton. ”However, the capacity buffer needed, due to trending inaccuracies, is often greater than the cost of performing a more accurate capacity forecasting analysis.”

In many cases, it also can be achieved without having to buy software or learning new skills. If a company owns a network and systems management (NSM) package, for example, it probably already has the tools needed to gather the utilization figures required for trending. Examining the graphs of network traffic, storage or CPU utilization, will give someone a rough idea of when to upgrade.

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If the company doesn’t have an NSM in place, however, it lacks the basis for predicting overload and bottleneck.

”We had issues where certain elements were becoming over-utilized or saturated,” says Benjamin Natal, network engineer for the Sheridan Press in Hanover, Penn. ”We needed to implement a capacity planning process covering our critical systems — key servers, network segments, routers, switches, T-1 links — that would let us be proactive in managing our resources.”

There are a variety of trending tools on the market that can do the job. These include Trending Manager by Qualitech Solutions of Charlotte, N.C.; Orion by SolarWinds of Tulsa, Ok.; Denika by Somix Technologies of Sanford, Me., and Expert Observer by Operative Software Products of Los Angeles.

Sheridan chose Denika and got it up and running in a matter of hours. In addition to using it for the original purpose of capacity planning, Natal says he also has configured the software to identify and resolve network bottlenecks, and to keep a watch on server disk utilization so he can clean up a disk before it affects performance.

Blending Art and Science

While trending provides a basic form of capacity planning and is useful in certain situations, it has its limitations.

As British statesman Edmund Burke once told a member of Parliament in 1791, ”You can never plan the future by the past.”

Trending does not take into account discrete events, such as layoffs, mergers, network upgrades or replacing direct attached storage with a storage area network (SAN). Nor does it take into account the characteristics of a given piece of equipment under different traffic loads. Going from a single-CPU server to a four-way box doesn’t result in four times the throughput.

Accurate capacity predictions require the use of more sophisticated tools, which let the user model different scenarios and see the results. These tools do not model the entire infrastructure, but focus on a certain aspect of it. Here are some examples:

Drew Robb

Originally from Scotland, Drew Robb has been a full-time writer for more than 25 years. He lives in Florida and specializes in IT, engineering, and business. As well as eWeek and TechRepublic, he writes for a wide range of magazines including Gas Turbine World, SDxCentral, and HR Magazine. He is the author of Server Disk Management in a Windows Environment (Auerbach Publications).

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