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The Green Grid takes a look at data centre metrics and what governments need to know about data centre energy efficiency
 Being able to measure current energy efficiency and quantifying the affects of subsequent changes, is fundamental for any government to truly understand and maximise data centre energy efficiency.
We all understand the value of common measures that can demonstrate to stakeholders how efficiently and cost effectively data centres are running. These metrics are very important in showing how much data centre technology has advanced in the bid to curb adverse effects on the environment and boost productivity.
Establishing a common metric for measuring data centre efficiency and developing guidelines as to how the results of this measurement can be improved is still very much a work in progress. It is a key element of the work of The Green Grid.
No universal measure
Data centres are not like cars where there is a universal measure that everyone understands and relates to, for example ‘miles per gallon’. Data centres are complicated machines; they’re often built and upgraded in piecemeal fashion and added to and modified according to the business need. The factors are too many and variable to make developing measurements easy, which is why the measurements we are developing will be subject to constant evolution and improvement.
Setting up these metrics is one of the most important remits of The Green Grid. We need metrics that can be accepted and respected by everyone in the industry, so we can at least get an accurate picture of how data centres are performing in a bid to develop best practice guidelines. We published our first whitepaper on the Data Centre Infrastructure Efficiency (DCiE) and Power Usage Efficiency (PUE) metrics in 2007, and we’re happy to say these two standards have now been included in the European Commission’s Code of Conduct on Data Centre Efficiency.
This is a very important step in ensuring these best practice guidelines are adopted by governments and businesses alike and will help data centre managers move towards a more accurate measurement of their energy use. This is important not just in terms of protecting the environment, but also managing costs. Data centre power and cooling are two of the greatest issues facing IT departments and governments need to control these costs while maintaining the option of expanding, if they are to remain strong.
The first thing to note about the Data Centre Infrastructure Efficiency (DCiE) metric is that it is a redefinition of the previous Data Centre Efficiency (DCE) standard. We found that DCE in particular had not received broad uptake due to a misconception of what it really means. Both DCiE and PUE represent tactical measures that IT departments can implement now to tell if it is possible to optimise the data centre before determining if they need a new one.
‘DCiE’ and ‘PUE’
Both of these metrics are simple in the way they work but naturally depend on the use of accurate and honest information. The PUE is defined as Total Facility Power divided by IT Equipment Power, while DCiE is defined as IT equipment power divided by Total Facility Power. These terms mean something quite specific.
Total Facility Power is defined as the power measured at the utility meter, or the power dedicated solely to the data centre (rather than power used by other functions of a building housing the data centre). This includes everything that supports the IT equipment load such as:
- Power delivery components such as UPS, switch gear, generators, PDUs, batteries and distribution losses external to the IT equipment
- Cooling system components such as chillers, computer room air conditioning units (CRACs), direct expansion air handler (DX) units, pumps and cooling towers
- Compute, network and storage nodes
- Other miscellaneous component loads such as data centre lighting.
If the data centre is housed in a building being used for other purposes, the data centre manager should be careful to exclude power being used elsewhere in the building. This involves calculating how much power is being used by other facilities and removing it from the total power consumed.
The IT Equipment Power is defined as the equipment that is used to manage, process, store or route data within the data centre. This includes the load associated with all of the IT equipment, such as computer, storage and network equipment, along with supplementary equipment such as KVM switches, monitors and workstations/laptops used to monitor or otherwise control the data centre. IT Equipment Power should be measured after all power conversion, switching and conditioning is completed and before the IT equipment itself.
The PUE can range from 1.0 to infinity. Ideally, a PUE value approaching 1.0 would indicate 100 per cent efficiency (i.e. 100 per cent of power is being consumed by IT equipment). We don’t currently know how data centres across Europe are faring in terms of PUE, but some preliminary work suggests many have a PUE of 3.0 or more, but with proper design can achieve 1.6. These numbers also don’t explain what constitutes an efficient or inefficient data centre. In the future The Green Grid will offer values that profile target PUE and DCiE metrics for a variety of typical data centre configurations.
What’s next?
Data centres are a complicated mix of IT equipment and facilities, which is why we’re developing metrics that will more accurately measure only what is used by the data centre. A mixed-use building may house any number of functions, such as data centres, labs, offices etc. For these types of mixed-use environments, determining the power usage of just the data centre environment is difficult. This is particularly true when the utility power grid enters the building through a single entrance point (eg through a utility room) and is then distributed to various building locations.
The latest cooling technologies integrate cooling elements such as pumps, refrigeration, blower and heat exchangers within the IT equipment itself. These technologies blur the lines between what has traditionally been a clear delineation between facility equipment and IT equipment. The Green Grid will provide clearer distinctions between facility and IT equipment and recommend power consumption measuring techniques throughout the data centre, as well as for the equipment itself.
These measures will include Data Centre Productivity (DCP). This is a progression from PUE and DCiE that would divide Useful Work by Total Facility Power, in other words how much work can the IT equipment do in my facility. Productivity is a particularly difficult metric to determine, but is a key strategic focus of the industry and difficulty should be no reason not to attempt it. The calculation defines the data centre as a box; power goes into the box, heat comes out, data goes in and out and the box does a net amount of useful work.
The Green Grid is also considering the development of metrics that provide more granularity for the PUE and DCiE metrics by breaking them down further into components. This will help address the blurring of the lines between the IT equipment and facility infrastructure.
The measures we have at the moment are a work in progress, and we are working hard to refine them in consultation with the IT industry. Widespread adaptation of the metrics will help paint a better picture of where data centres are succeeding or failing in terms of power consumption and efficiency and this is why the European Commission’s decision is welcome and timely. |
