Power outage shuts down websites - A San Francisco data center's supposedly crash-proof system puts customers in the dark.

A power outage in San Francisco on Tuesday afternoon gave a glimpse of what it might be like as a swath of Internet websites went dark.

For hours, no one could find an apartment on Craigslist.org or buy a present for Mom at RedEnvelope.com. No one could Yelp or emote on LiveJournal. For hours, the 8 million virtual residents of the Internet fantasy site Second Life were inert.

A San Francisco data center that touts its double-backed-up system for protecting websites from crashing during power outages failed anyway on Tuesday, taking down with it Internet sites as popular as Craigslist and RedEnvelope, and raising questions about how safe the Internet is from power disruptions.

Just after 1 p.m., 40,000 San Francisco businesses and residents were affected by power fluctuations caused by an open circuit breaker, according to a spokeswoman at Pacific Gas & Electric Co.

For most companies, it meant inconveniences. At some firms, employees were sent home.

But Internet businesses, which promise to be open every day and at all hours, depend entirely on servers and their backups. Many San Francisco Internet firms use servers at 365 Main Inc., which says it provides seamless backup in the case of a power outage. "How safe is your data?" reads a company ad in the firm's San Francisco lobby.

This time, the Internet firms found themselves in the dark.

"It was right in the middle of the U.S. workday, so it was very bad for us," said Derek Gordon, an executive at the popular blog-tracking site Technorati, which experienced a total shutdown from about 1:50 to 3 p.m.

"It exposed a larger vulnerability," he said. "If this could happen to such a collection of major websites, what would happen if this was part of a major catastrophe? This was sort of a wake-up call."

Miles Kelly, vice president of marketing and strategy at 365 Main, said the company switched to backup power, although some customers were temporarily affected by the outage. He said the company would discuss the power failure once it knew more.

RedEnvelope's site, which handles most of the gift retailer's business, was down for more than three hours. The outage happened the same day that 365 Main distributed a news release announcing that RedEnvelope had shut down its "redundant" data center in the Midwest and was thrilled with 365 Main after "two years of continuous uptime."