Fujitsu is looking to optical fibre to help increase efficiency in the cooling of large datacentres. The company has developed a prototype monitoring system that can measure the temperature in up to 10,000 points using a single optical fibre connected to a measuring device.
It works by sending pulses of light down the fibre, which is laid around the datacentre and through the server racks, and measuring the minute amount of light that is sent back down the line due to Raman scattering, says Fumio Takei, a research fellow at Fujitsu who has been working in the system.
(Raman scattering is a process by which, when light is scattered from an atom or molecule, a small minority of photons are scattered by an exictation, resulting in them having a lower frequency than the other photons. The scattering is used as a tool in scientific research).
The intensity of the light varies depending on the temperature, so this can be used to estimate the temperature along the fibre, while the time it takes to come back can be used to measure the distance from the start of the fibre. Combining the two together means that the temperature can be estimated at numerous points along the fibre.
The basic idea isn't new and fibre-optic cables have been used for some time to monitor the temperature of things like tunnels, but the resolution of the system has never been precise enough to be useful in a datacentre, says Ei Yano, president of Fujitsu's device and materials laboratory.
The Fujitsu system is accurate to within half a degree Celsius and one metre. The temperature range that can be measured is between -10 degrees and 300 degrees Celsius.
In a demonstration at the company's research and development laboratory near Tokyo, a fibre was strung around a small server room and displays showed temperature read-outs for each rack starting at 32.4 degrees at the bottom of the rack and rising steadily — 33.9, 34.1, 34.4 and 35.9 — to 37.8 degrees at the top.
Fujitsu says the system can be used with fibre-optic cables up to 10 km long and at one-metre resolution that means approximately 10,000 points can be measured.
The company hopes to commercialise the system sometime in 2009. There is no word on price but Yano says such a system isn't likely to be cheap but comparably good value for a 10,000-point measurement system.
As computers get more powerful, the amount of heat generated by them is increasing, making datacentre cooling a more difficult job. The new technology should be able to help better employ cooling systems so hot areas are more efficiently cooled and less power wasted.
An added benefit is that the system relies solely on light and not electrical measurements, so stringing the cable close to servers won't cause interference.