Inside the centers, the drill during a natural disaster can be overwhelming. One company, EdgeConneX, lost utility power for three days at a Miami data center, two days at a center in Jacksonville, Fla., and two days at an Atlanta location. But Rich Werner, director of operations at the company, said that backup generators turned on and service was never interrupted.

“Data center operations, to me, is 362 days of boredom,” Mr. Werner said. “And then you get these hurricanes coming through, and it’s three days of pulling your hair out.”

There are no legal standards for data centers unless they house servers for clients like government agencies, which require special protections.

But a professional organization, the Seattle-based Uptime Institute, rates the facilities on four tiers of resiliency for events like storms, earthquakes and run-of-the-mill power failures — possibly one reason the internet performed creditably during the hurricanes. The institute’s engineers “go to the site and pull the plug,” said Mark Harris, senior vice president of marketing, “and to be certified, it has to keep running.”

“So when a hurricane or a tornado or an ice storm happens, the entire data center has been designed to withstand these external factors,” he said.

During Harvey and Irma, those measures seemed to work, said Doug Madory, director of internet analysis at Dyn, a web performance company with servers at a Miami data center. “I’m not aware of any core internet services going down,” he said.

One necessity is building above the 500-year floodplain, according to Gary Wojtaszek, president of CyrusOne, whose facilities include a data center in the mostly flooded Galleria area of Houston. The water stopped a few feet short of the building, which ran on backup power for several hours, Mr. Wojtaszek said. He added that “practically every single large oil and gas company in the world” operates servers in its data centers — an indication of how commerce of all kind relies on the facilities.