As I have mentioned in the last couple of posts we have been looking at the provision of additional Data Center capacity for a client along with the creation of a program to decouple the growth in IT and power usage from business growth.
A lot of the focus of this work has been around using the Power Usage Efficiency (PuE) metric of both the new facility as well as how we can improve the existing Data Center estate. The metric has been a great way to explain to senior management the impact of some of the changes, and occasionally the benefits that they will see in environmental and economic efficiency.
We have however had a number of issues with PuE, mainly caused by the planned use of a Tri-generation capability for both power and cooling delivery. The number has also been skewed dramatically as we are looking at a solution that can, when the conditions are right, make use of outside air for cooling.
This has got me thinking that maybe the focus that the Data centre industry has at present on PuE is somewhat misguided. Although the metric is doing a great job at getting some commonality into discussions it is very easy to “cheat” the numbers. Should we be reporting the number without the “cost” of the cooling we get as a by-product of power generation? What about reporting the metric based on the coldest possible day? How do we account for the power contained in the gas when compared with the grid provided electricity?
The idea that we are looking at, and aligns with some of the ideas being discussed across the industry (for example on Dava Ohara’s blog), is using not the data-centre power but cost as the key number for analysis. Trying to compare the overall costs of operating the data centre with the cost associated with the operating the IT environments that it contains provides a very interesting data point for management, which is picking up the name Cost Usage Efficiency (CuE). We are still working on this, but hope to include not just the operational costs but also the capital costs associated with both the facility and the technology.
By Andrew Skinner, UK Data Center Technology & Operations