There's a maxim in the data centre business that you can't manage what you can't measure, and eBay has come up with the mother of all measurement systems for calculating data centre efficiency.

The online auction giant devised its Digital Service Efficiency methodology to look at the cost of its IT operations in dollars, kilowatt hours and carbon emissions, and ties those costs back to a single performance metric - in eBay's case, the number of buy and sell transactions its customers make at

The result is a set of data that provides the equivalent of a 'miles per gallon' metric for data centres, which organisations can use as a baseline to improve on over time, said Dean Nelson, head of eBay's Global Foundation Services, which manages its data centres worldwide.

"eBay is a single system, it's the sum of a million parts, and we needed a way to measure and convey the efficiency of this system," he said at the Green Grid Forum, a data centre efficiency conference in Santa Clara, California.

Power Usage Effectiveness

eBay has published the methodology in the hope that other companies will adopt it too, much as the industry rallied around Power Usage Effectiveness, or PUE, as a general metric for data centre efficiency.

eBay's system, which it calls the Digital Service Efficiency (DSE) dashboard, goes further than PUE, measuring its IT infrastructure and relating it to the four metrics its top executives care about most - revenue, performance, environmental impact and cost.

In the process of sharing its method, eBay took the unusual step of releasing a wealth of data about its own data centres. It operated 52,075 physical servers at the end of last year, and generated 740 metric tons of carbon per million users, or 1.6 tons per server.

It set itself a target of reducing its cost per transaction and carbon emissions per transaction by 10% this year, and of increasing its transactions per kilowatt hour by the same amount, Nelson said. It shared those figures too - apart from the costs in dollar terms, which it views as competitive data.

Google efficiency data

"We're not going to show our detailed profit and loss numbers to everyone; we're devising a metric to show how much we're improving efficiency each year," said Rohini Jain, finance lead for eBay's technology infrastructure.

Still, it's more data than most other companies provide. For instance, Google doesn't disclose how many servers it operates or how much power its data centres consume, though it does publish efficiency data.

It may not be easy for other companies to replicate eBay's methodology. EBay has a straightforward metric against which to measure performance - the number of transactions its customers make, which it measures in URLs - while many other firms have more complex business models.

It also helps that it is a technology-driven company willing to invest in energy-saving ideas. It brought its first solar farm online in December, generating 650 kilowatts of power, and it plans to install Bloom fuel cells later this year that will provide up to 6MW.


The software, hardware, operations and finance teams at eBay are working together on the project, Nelson said. In one experiment, its software developers adjusted the memory utilisation for a pool of servers, allowing it to eliminate 400 machines and save a megawatt of power, he said.

PUE was controversial when it was introduced by the Green Grid Forum six years ago, Nelson said, but it has since been adopted widely.

Like PUE, the 'miles per gallon' data isn't necessarily useful in and of itself, but it could give companies a benchmark to measure progress moving forward.

"We averaged 46,000 transactions per kilowatt hour last year. Was that good? We don't know, we have nothing to baseline it against," Nelson said.

This year, eBay - and everyone else - will be able to see how it's doing.