Rackspace, which offers a variety of hosting and for enterprise customers, suffered power generator failures on June 29 that caused customer servers to go down for part of the day.

Rackspace to the that it expects to issue one-time service credits to impacted customers totaling $2.5 million to $3.5 million. The final number hasn't been determined as Rackspace is "continuing to assess the financial impact of service credits due to these events."

The 144,000 square foot data center is in the Dallas suburb of Grapevine and is Rackspace's primary hosting location. Outages previously struck the facility in November 2007.

This time, Rackspace apologized to customers in a , saying the power outage was "the result of a range of power infrastructure issues," and that the company serviced its UPS units and generators after the incident. The power outage affected portions of the facility.

"Although we have had some issues with this data center before, please know that we will do what it takes to improve its reliability and performance," Rackspace said. "We owe you an action plan to prevent this type of thing in the future, and we'll get that to you as soon as it is ready."