Everyone knows the adage “there are lies, damn lies, and statistics.” This about the later, the statistics. When you are managing anything it’s true that you can’t improve what you can’t measure. So if you are trying to improve your IT business using virtualization, you need to accurately measure the percentage of your environment that *is* virtualized.

Most think this is an easy thing to calculate. However, as I discussed this topic with colleagues and clients it became clear that this number is not always a straight forward calculation and that many people were calculating it wrong.

As an example, take the following situation:

Acme Corporation had 550 servers before they started their server virtualization project. If, after the first phase of virtualizing Acme Corporation ends up with 100 physical servers with 50 of them running hypervisors supporting 500 virtual machines, what percentage of acme corporation’s computing environment is virtualized?

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Most people I talk to about this have falsely thought the environment was 50% virtualized. Half of the physical servers are running virtualized. But that doesn’t take into consideration that there are 500 work loads (computers) that were virtualized and condensed onto fewer servers.

So then the correct answer must be the one achieved by taking the number of physical servers divided by the number of VMs to determine the percentage virtualized. 500%. Wait, that doesn’t make sense. How can you be more than 100% virtualized? (exactly…)

So, what’s the correct answer?

91%.

Here is the correct formula:

% virtualized = VMs / (physical servers running non-virtualized + VMs)

You’re taking the total compute work loads (measured by Operating System containers) divided by the virtualized compute work loads. So 500 VMs / 50 physical servers + 500 VMs = .909090 or 91% (ok, ok…so I rounded up to try and throw you off.)

So next time IT management asks you “What percentage virtualized are we?”, you’ll know how to correctly answer.

Chad Jenison says

i think the formula is wrong, even though the answer is right (percentage).

Your formula yields 1.1 by my math, so you’d to do 1/x or alter the formula to:

% virtualized = VMs / (physical servers [non-vritualized] + VMs)

so in this example .91 = 50 + 500 / 550

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Chad Jenison says

oops; .91 – 500 / 50 + 500 -> 500/550

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latoga Reply:

April 9th, 2009 at 3:15 pm

Nice Catch Chad! I had the numerator and denominator swapped. That will teach me to not write a major blog post on my iPhone… I fixed the formula in the post.

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