Microsoft Shares Insight on its Data Center Chargeback System

The Power of Software blog has a new post by Amaya Souarez.  There is so much information in this post, it is hard to summarize, so let’s start with a list, extracting words from the post.

  • Green is a priority.

I believe that implementing chargeback models based on power usage will encourage customers to consider power efficiency more seriously and reduce our overall impact on the environment.

  • Interesting analogy

I would like to illustrate this point by using the analogy of getting a first car for a teenager. By the way, if you currently have one of these creatures at home, then you have my commiserations.

Comparing Chargeback Models

Let’s say you are investigating the conditions under which you will allow your teenager to have a car. Consider the following two options:

  1. The teenager buys the car, but you pay for the gas.
  2. You buy the car and the teenager pays for the gas.

For each option, what sort of car do you think your teenager will want?

With option 1, you may find that they come back with a clapped out 351 cubic inch monster with the thirst of a Jentil, maybe something like the “striped tomato” from Starsky and Hutch. And who cares? You’re paying for the gas, right?

But there’s no point in having the coolest car in the neighborhood if you can’t even afford to take a date to a drive-in movie. If you select option 2, you may find your teenager develops a more healthy interest in how many miles per gallon (MPG) something more sensible can manage (like the new Prius hybrids at the Redmond Campus), rather than whether they have enough torque to leave tire slicks longer than a 747 landing at Princess Juliana International airport.

  • Statement of the problem.
  • With servers, the situation is more complex; the main issue that we struggle with is the fact that there is no direct equivalent to miles per gallon. How do you measure application output? It isn’t just about CPU utilization. What about an application that makes repeated calls to hard disk but doesn’t use much in the way of processor resources? If you fit more memory to the server, it can may be able to cache the disk access calls, but you’re then consuming more power in the additional memory module.

    All the standard performance monitoring areas, such as processor, memory, hard disk, network, and cache make varying contributions to power consumption. What we needed at Microsoft was a chargeback model that is easy to understand, straightforward to administer, and allocates data center costs to customers proportionately.

  • Confession of the issues.

For the Microsoft data centers, the effort to change our chargeback model was not a simple conversion, as it took us one and a half years to move from  our previous model of charging for floor space based upon rack utilization to the new model. Not surprisingly, it was not the tooling or process modifications that posed the biggest hurdle but the cultural and political changes that were required. Even today, I frequently have to remind customers that ‘DC space is power.’

  • Final action.

The final model that we now use has two basic components:

  • Floor Space. This component is billed per kilowatt (kW) of usage and includes all the floor space costs.
  • Power and Cooling. This component is billed per kilowatt hour (kWh) of usage and includes the cost of electricity as billed by our energy suppliers.

I’m not using real figures here, but you should be able to see the basis of how we implemented charging based on power consumption.

And there is plenty more in the blog entry.

Amaya Rocks!

Here are her final words.


Changing our chargeback model to one that uses power as the basis for floor space makes sense, both for us and for our customers. As older equipment is retired and replaced, we expect to see greater emphasis on power efficiency rather than raw output. Reducing power consumption on individual servers results in a reduction in the total power consumption for the data center, helping to conserve our power bandwidth and minimize our impact on the environment.