PUE, DCiE, what’s it all about?

PUE is a metric developed by The Green Grid to measure Power Usage Effectiveness, which compares the total facility power usage against the IT power load. DCiE (Data Centre infrastructure Efficiency) is simply the inverse of PUE reported as a percentage. What do these figures actually tell us? They give a snap shot in time of a data centre or computer room's power use which can be used to suggest how efficiently your data centre's plant equipment is running. One of the main problems with PUE and DCiE is that the results tend to vary depending on the weather conditions at that particular moment in time. For example, if you took PUE measurements at 6am and again at 2pm, the difference in outside temperature and humidity would affect how hard your plant would have to work. A higher outside temperature requires air conditioning chillers to work harder to cool the same load, which has a significant impact on power usage. To make effective use of PUE and DCiE, reading need to be taken regularly to get an averaged result.

OK, so now we are in recession. There are, and will be more, calls for spending cuts and more efficiency from existing hardware and our staff. PUE and DCiE can play an important part in this. But where to start? As we are talking data centres, look at the power consumption. Or more accurately, look to see if you can look at the power consumption. It is amazing how many data centres and computer rooms, even the new builds don’t have metering installed to monitor power consumption. Data centres are estimated to contribute 3% of the CO2 emissions globally, yet the vast majority of data centre managers have no idea how much energy their facility consumes – let alone where to start making savings.

How do you get on with your company’s Facilities Manager? Putting that aside, it’s imperative that there is a good working relationship between these vastly important departments (IT and Facilities) as these two hold the key to reducing energy consumption, and therefore costs, more than any other department. Look at it from the Facility’s Managers point of view. He has little if any impact on what is installed in the data centre. All he or she will see is the monthly or quarterly electricity bills coming in with little idea of where to reduce costs, or indeed, where the costs are coming from. Keeping him/her in the picture is incredibly important. Working together to install electricity meters to enable the PUE and DCiE to be calculated and logged on a regular basis is a start. It is also imperative to log your consumption regularly by taking meter readings and trending the power usage, what impacts it and what changes it.

How much will you save by installing this meters? Without proper metering, who knows?

Migration Solutions is a member of The Green Grid which is focused on advancing efficiency in data centres. They have also recently received Information Age's award for Best Data Centre Innovation 2008 for ERA - an Environmental Report and Audit which aims to help data centre owners to save money and the environment with no or little financial outlay.