A massive power outage in San Francisco yesterday that was caused by a faulty transformer took many high profile web sites, including classified ads site Craigslist.com, offline for a number of hours.

Datacentre co-location provider 365 Main saw its systems pack up after the power cut. Its customers include Craigslist.com, Cnet.com and SecondLife.com. Investment bank Charles Schwab uses 365 Main’s data centre to support some financial transactions, while Sun Microsystems uses some of its resources as part of its utility grid service. However, not all of these customers reported a disturbance in service.

"There was a major power event in San Francisco that impacted business operations for many San Francisco based companies, including 365 Main's San Francisco datacenter,” the company said in a statement.

“Some customers within the 365 Main facility were temporarily affected by the utility failure. The building is currently 100 percent operational and running on backup power [generators] until the company can confirm that utility power is stable."

The incident raises fresh concerns about data centre power supply, and whether systems that need to be constantly available should be powered by public electricity supplies.

The impact on businesses across the world, however, could have been greater had more software-as-a-service providers’ data centres been located in the area.

Earlier this month, SaaS finance package provider NetSuite revealed that it only has one data-centre, which contains all its customers’ records and supports their instances of the application, located in an earthquake prone area of California.

The possibility of outages like that witnessed yesterday in San Francisco will do little to assuage the caution with which many IT managers view software-as-a-service application providers.

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