Fuel was in short supply, however, as was other equipment such as power cables, which the government directed to the most hard-hit areas. 'You couldn't get a normal power cable with a power strip for one month," he said.

Power shortages remains the biggest problem. The government has reactivated hydro and fossil fuel plants, but starting July 1 all facilities that consume more than 500kWh are ordered to reduce their peak power usage by 15 percent from a year earlier.

Data centers operators have fought the cap with some success. They argued their facilities are critical infrastructure and that many had already slashed their consumption before the earthquake as part of energy-efficiency projects. Also, companies have been "evacuating" servers and storage from Tokyo offices to their data centers because of power shortages in the capital, making it even harder to reduce demand, Yamanaka said.

"We told the government it was physically impossible" to meet the reduction targets, he said. The government eventually backed down and has reduced the target for data centers to between zero and 15 percent, depending on how much they reduced energy use the year before. Fines for noncompliance are high -- the equivalent of US$12,500 for each hour over the limit.

Power problems are likely to worsen this summer when cooling systems work overtime, and could lead to further rolling blackouts.