Blades point up datacentre cooling inadequacies, say analysts

The rapid uptake of high-density blade servers will force IT leaders to rethink cooling provision in their datacentres over the next five years, warn Gartner analysts.

High-density blades are the fastest-growing segment of the server sector, according to the advisory firm. But even datacentres built as little as five years ago were not equipped to deal with high concentrations of blades, according to Gartner's report on the subject.

That will have consequences for cooling and space requirements and how server life cycles are managed.

Traditional datacentres were designed to have a uniform energy distribution of around 2 to 4kW per rack. A rack of industry-standard servers needs 30sq ft without supplemental cooling, and a rack that is 60 per cent filled could have a power draw as high as 12kW.

With the increasing use of high-density blade systems, this design envelope is no longer sufficient, says the report, because traditional forced-air cooling methods become increasingly ineffective at densities above 15kW per rack.

Any standard rack of blade servers that is more than half full will require extra cooling.

Gartner is recommending the adoption of high-density zones in the datacentre to provide the best method to balance the power and cooling requirements of different IT equipment – such as servers, storage and networking boxes – in the same physical room.

The firm defines a high-density zone as one where the energy needed is more than 10kW per rack for a given set of rows. It predicts at least half of all datacentres will feature a high-density zone by 2015, up from one in 10 last year.

A high-density zone will typically require supplementary cooling, such as a chilled-water system, hot/cold aisle containment or in-row/in-rack cooling, says the report.

Datacentre managers have yet to be convinced of the efficacy of high-density zones, said Rakesh Kumar, research vice-president at Gartner: "Many users remain unsure of the benefits of high-density zones – especially in gaining flexibility in capacity planning – as well as the potential pitfalls."

The issue has come about largely because a datacentre building, its power and cooling systems, and the IT equipment it contains operate on three different life cycles.

"Over a 15-year period, a building will remain essentially the same, but the electromechanical systems will typically need one round of modifications, while the IT systems will typically be refreshed two to three times," said Kumar.