Feb 28, 2014

What are the most common mistakes during network capacity planning?

When conducting network capacity planning, what are the most common mistakes? After all, a plan that looks good is pretty useless if it is build on a weak foundation and mistaken assumptions. Any tips?

Top 10 Capacity Planning Mistakes

"I’ve listed some of the common mistakes when capacity planning is done by organisations who don’t have experienced capacity planners. I’m interested in other people’s feedback on these mistakes.

Ordering hardware without understanding the existing utilisation
Treating all CPU utilisation as the same – there are different types of drivers of CPU utilisation, e.g. ‘hum’, iowait, OLTP and Batch. I have seen people assuming the business is going to see a doubling of demand and assuming the CPU utilisation will also double. In this calculation they may include ‘hum’ and batch CPU utilisation.
Including iowait in CPU utilisation when it is usable CPU capacity and excluding it when it isn’t
Not understanding the workload characteristics before ordering new hardware. Sounds unlikely, however this does happen. I worked on an engagement some years ago where the organisation purchased brand new Blade servers for their application only to realise that their application was disk I/O intensive. The new Blade hardware didn’t provide any increase in the disk I/O throughput capability.
Forgetting about Moore’s law when doing a hardware refresh. This is also related to the previous mistake. I have seen organisations doing a count of the number of servers for CPU intensive applications and then ordering the same number of new servers even when the new servers have a fourfold increase in CPU processing power."

 I think one of the most common errors is spending a lot of time and effort trying to come up with future projections that are really based on unknown variables, then treating the results as facts when it is really little more than a guess. It’s like anything else, once you get intellectual “lock-in,” it is very often difficult for people to step back and reassess it objectively and logically. A non-IT example would be people who deny climate change - they just can’t separate how they feel from facts. I see it in future growth projections for businesses as well. I was having a conversation with someone starting a webzine. They had little to no name recognition, very little funding, and a modicum of talent. Nevertheless, they were planning on going from zero to a million unique visitors per month in one year. I know this isn’t networking, but it’s the same idea - planning based on unrealistic projections is not really planning. 


There is a good overview on this topic at Microsoft’s Technet library that lays out some of the planning and pitfalls of network capacity planning -  http://technet.microsoft.com/en-us/library/cc767907.aspx

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