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The Art of Capacity Planning by John Allspaw

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Chapter 3. Measurement: Units of Capacity

The only man who behaves sensibly is my tailor; he takes my measurements anew every time he sees me, while all the rest go on with their old measurements and expect me to fit them.

George Bernard Shaw

IF YOU DON'T HAVE A WAY TO MEASURE YOUR CURRENT CAPACITY, YOU CAN'T CONDUCT capacity planning—you'll only be guessing. Fortunately, a seemingly endless range of tools is available for measuring computer performance and usage. I'm willing to bet that moments after the first computer program was written, another one was written to measure and record how fast the first one performed.

Most operating systems come with some basic built-in utilities that can measure various performance and consumption metrics. Most of these utilities usually provide a way to record results as well. Additional popular open source tools are easy to download and run on virtually any modern system. For capacity planning, your measurement tools should provide, at minimum, an easy way to:

  • Record and store data over time

  • Build custom metrics

  • Compare metrics from various sources

  • Import and export metrics

As long as you choose tools that can in some way satisfy this criteria, you don't need to spend much time pondering which to use. What is more important is what metrics you choose to measure, and what metrics to which you pay particular attention.

In this chapter, I'll discuss the specific statistics you'll want to measure for different purposes, and show the results in graphs to ...

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