Calculate How Well Server Virtualization Reduces Energy Consumption


Many IT managers are under pressure to green their data centers and help reduce their company's carbon footprint. In practical terms, this means reducing energy consumption. This Green Data Center Calculator gives you a quick approximation of the results you can expect from server virtualization.


Here is an in-depth look at this useful calculator and all of the benefits it can offer.


This calculator provides a Power Usage Efficiency number-total data center power consumption divided by server power consumption - which is widely used to gauge data center efficiency. A PUE of 2.0 means that it takes twice as much power to operate the data center as it does to power the servers. According to The Green Grid, a PUE of 1.6 is achievable. In other words, the lower, the better.




To begin using the calculator, understand its assumptions.


  1. Non-server costs consist of the following components, shown with the percentage they are assumed to contribute to the total non-server cost, i.e., the portion of the total utility bill not directly associated with server power consumption.
    . Chiller 47%
    . Universal Power Supply (UPS) 26%
    . Computer Room Air Conditioning (CRAC) 13%
    . Power Distribution Units (PDUs) 7%
    . Humidifiers 4%
    . Miscellaneous 3%
  2. The power consumption of non-server components varies proportionally with the power consumption of the servers.
  3. The previous item (2) is only true if the chiller is equipped with variable frequency drive (VFD) technology. If not, then server power consumption variations do not affect the chiller.
  4. Server power consumption can be reliably estimated by the following formula: Pn = (Pmax-Pidle)* n/100 + Pidle. Pn is power consumption at n percentage CPU utilization,Pmax is the maximum power draw, and Pidle is the power draw at idle.


In addition to these assumptions, a little data homework before completing the calculator is needed.


  • Measure the power at the point it enters the data center, even if this requires the installation of a new meter.
  • Determine the power consumption of each server at full load and at idle. These figures are often available from manufacturers, but make sure you get the actual power consumption, not the power supply rating, which will be much higher. If you need to obtain measurements yourself, you can do so for each server type you've standardized on. It's not necessary to measure every server.
  • Obtain CPU utilization data for each server. This is typically collected by systems management software.
  • Find out if you have variable frequency drive (VFD) chillers. Cooling and power conditioning/distribution units typically draw substantially more power than the servers themselves, and chillers are particularly big users. Chillers equipped with VFD technology have a power draw that's proportional to server power consumption. Those that lack VFD may not exhibit any power reduction in response to reductions in server power.


This data, which should be entered in the white cell fields of this spreadsheet, will help calculate the data represented in the yellow fields (see the screenshots below for the white and yellow fields). To begin, save the calculator using a new name. This is important if you want to use the calculator for multiple what-if scenarios because it does not reset automatically. Next, at the RESULTS tab, enter the amount of the total monthly utility bill (power usage data) in the "Utility Bill" cell.


Then, click on the INPUTS tab.




At the INPUTS tab, enter the following information:


  • In the Asset List column, enter designations to replace, "Server 1," "Server 2" etc. (This is optional.)
  • In the Y/N column, enter a "Y" for every server that has an application that is potentially eligible for virtualization, and an N for "sacred servers" that cannot be part of a virtualization program. If fewer than 100 servers are part of this calculation, make sure that cells that have neither a "Y" nor an "N" are left blank.
  • In the Pmax column, enter server power consumption at full load.
  • In the Pidle column, enter server power consumption at idle.
  • In the Old % Utilization column, enter the average CPU utilization. Make sure that utilization numbers are entered only for servers that are part of this calculation (the "Y" servers). All other servers should have a utilization of 0 %.
  • In the Price/kWh column, enter the appropriate figure (for Server 1 only).


Finally, head back to the RESULTS tab. First, enter your desired headroom. For example, if you enter 20 percent, the calculation will assume that no server should operate at more than 80 percent of capacity. Second, enter "Y" or "N" in the "Chiller VFD?" cell.


All appropriate calculations will be finalized once that last bit of data is entered.


As a bonus, the last tab, titled "ECO," gives a quick look at how you can improve your carbon footprint by telecommuting. Enter your average commute in miles and the automobile's miles per gallon figures. Those numbers reveal (in tons and pounds) how much carbon dioxide was not released into the atmosphere. In addition, the calculator reveals how many acres of trees would have to be planted to achieve that reduction in carbon dioxide.


ECO tab