Data centre energy efficiency has been getting an enormous amount of attention recently.

While some companies on both the buy and sell sides are treating the issue as 'green IT', the fact is that there are a number of drivers, not least of which is the realisation a few years ago that fully loaded rack systems have the ability to boil a kettle almost as fast as they can process a transaction.

The inability physically to increase rack density due to cooling considerations was a real show-stopper toward high density distributed computing.

For those of us who started our IT careers back in the days of IBM big iron there is a certain irony in the re-emergence of huge cooling and machine room air-con as enablers for continued data centre growth.

In addition to the cooling concerns, data centres are also short on go-go juice. Approval for new data centres in London has been put on hold as utility companies cannot keep up with the demand for power.

With London busy planning and building for the 2012 Olympics the electricity requirements of the future games venues are taking priority, while any new data centres are finding themselves towards the bottom of the customer priority list.

The problem of available cheap electricity is not confined to Olympic cities. China and India are ramping up their computing capabilities and requirements, while energy supplies are already constrained.

South Africa's largest city, Johannesburg, is suffering daily scheduled energy cuts due to the complete inability of the power suppliers to meet current demand.

The power companies euphemistically call this "load shedding", a term in which the local business leaders manage to find humour as they sit in unlit meeting rooms and drink pre-brewed coffee from a thermos.

Less amusing is the ongoing economic meltdown resulting from the power supply constraints, which are expected to continue for at least four years.

For Johannesburg the end of cheap and abundant energy supply has already arrived, and the city serves as a test-tube example of what faces many other cities unless the rate of increase in energy use is reined in.