Water cooling is back. HP recently detailed a water-based cooling system for its high-density servers and a standardised server rack that replaces seven existing models and will be the base platform for the cooling technology.

HP's move into fluid-based cooling follows IBM 's release last July of an add-on water- cooled unit for its server line. And more recently, blade server maker Egenera announced an offering called CoolFrame that integrates Liebert's X-treme Density (XD) cooling technology with a new 24-blade enclosure.

Liquid cooling, once a staple of mainframe-oriented data centres, is returning to the mainstream as some IT managers look for ways to keep their increasingly dense and power-hungry servers chilled.

"I think liquid cooling is here to stay, and customers will want standardization -- plug-and-play capabilities," said Paul Perez, HP's VP of storage, networking and infrastructure.

Perez said HP is talking with rival vendors as well as standards organisations about the need for things such as standardised fittings for tapping into chilled water supplies. "What we're after is some consistency of experience for customers," he said.

But vendors' enthusiasm for liquid cooling will meet resistance from users like George Horvath, who manages Memorial Sloan-Kettering Cancer Centre's 18,000-square-foot data centre. "I'd prefer not to have any of those cabinets here," said Horvath, adding that facilities managers in particular are going to be worried about leaks. HP's Modular Cooling System is a self-cooled 42U rack that costs $30,500 and can cool racks of blades that consume up to 30kW of power. Because the unit is self-contained, it doesn't have to be located in a data centre and can be placed in air-temperature rooms, HP said.

Egenera said its third-generation BladeFrame EX enclosure uses x86-based processors in an integrated, virtualised system that allows computing resources to be allocated to applications as needed.

Liebert, which is a unit of Emerson Network Power, uses a coolant other than water in XD, an approach that it says is more efficient. The cooling technology adds about $300 to $400 per blade server to the cost of rack systems, said Susan Davis, Egenera's vice president of marketing.