Stop Making a Big Stink About Data Center PUE

Zahl Limbuwala is CEO of Romonet.

Data center managers are finding that their Chief Finance Officers are increasingly interested in the organization’s infrastructure. This is only natural; data centers represent a major investment for the business, and CFOs will want to be certain they’re getting value for money.

The challenge then is how to present this value to CFOs and sell them on a particular investment choice. Power Usage Effectiveness (PUE) has often been cited as the de facto indicator of data center performance, but the definition has been stretched to the point where it is almost unusable. As we know, PUE is the ratio of the energy taken in by a data center to that actually used by IT - with 1.0 being the impossible ideal. While this can give an idea of efficiency, it does not provide the full picture. Instead of focusing on abstract measurements like PUE, organizations should concentrate instead on delivering the best cost for the business.

Traps and Deadends

“Design” PUE is also not particularly useful. Instead of a realistic view of data center performance, it tends to show how a data center is run in its optimum state. Unsurprisingly, a data center may well never achieve this state in its lifetime, let alone immediately after it opens for business.

PUE makes two assumptions which cause problems. Firstly, that all IT load is good, and second that all IT equipment is of equal efficiency and value. If I have two data centers, one with an exceptional PUE but using IT equipment with no power management and hosting non-critical development platforms; and a second with a poor PUE but correct power management and hosting only essential business IT servers, I need to know more to understand which is actually the most efficient. In the same vein, a half-full data center will have a very different PUE to one running at full capacity, yet PUE won’t show which of these actually costs the business more. Another counter-intuitive example is turning equipment off overnight to reduce costs and emissions. This will worsen PUE since IT load has dropped while the power consumption of the data center remains constant, meaning managers may receive contrary reports that power saving measures are actually reducing efficiency.

Getting the Metrics Right

We shouldn’t assume that PUE is now worthless. Used correctly it can still give an impression of data center efficiency. However, organizations need to be sure that they are using metrics that will show the true value of their investment. The first step should be establishing the Total Cost of Ownership (TCO) of the data center. While aiming for better efficiency is all well and good, if this doesn’t result in improved profitability of services or reduced costs then there’s little point.

Secondly, we need to consider what value the organization receives from its data centers. To do this, you should use metrics that work in the context of what the organization wants to achieve. For example, a retail hub like eBay will be concerned about cost per transaction, while other enterprises might like to know the precise cost of each email inbox or other crucial business service. Once businesses know these costs, they can then optimize them; from which improved efficiency and reduced carbon emissions naturally follow.

As mentioned, the CFO is the ultimate decision-maker behind any IT investment. Their only concern is delivering IT at the lowest cost to the business and avoiding unnecessary investment. Being able to provide the precise, real-word costs for individual IT services, instead of more abstract figures such as PUE, will provide a huge benefit to data center teams pushing for investment (and fending off the challenge of the cloud with its clearly delineated costs).

Measuring Up

Unless PUE is used correctly and in the right context of business costs, it will be of most use as a marketing number. Effciencies in power consumption and management will instead follow if organizations aim at delivering the best TCO. Understanding the TCO of the entire data center estate; knowing whether this is in line with the business’s expectations; and being sure of what, if any, investment is required, will allow organizations to make the best use of their resources well into the foreseeable future.

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