Google has revealed that its March outage in Ohio was caused by an issue with its uniterruptible power supplies.

First reported by The Register, the outage occurred on March 29 and saw "degraded service or unavailability" for more than 20 services from the us-east5-c zone of Google's US East cloud region in Columbus, Ohio.

In an incident report shared by the company on April 11, Google noted that the outage lasted for six hours and 10 minutes and that the root cause was a loss of utility power in the zone.

The report explained that the power outage caused a "cascading failure" within the UPS system that was responsible for maintaining power in such an event.

"The UPS system, which relies on batteries to bridge the gap between utility power loss and generator power activation, experienced a critical battery failure," Google explained.

This left the UPS unable to perform its core functions, and virtual machine instances within the zone lost power. The incident report added that the power outage and subsequent UPS failure "triggered a series of secondary issues, including packet loss within the us-east5-c zone, which impacted network communication and performance," and brought down some storage disks.

To fix the outage, engineers bypassed the failed UPS and restored power via a generator just under two hours after being notified about the issue. Most services were recovered at this point, though some needed manual actions for full recovery.

Google noted that it was taking steps to prevent such an outage from occurring again, including looking to harden the cluster power failure and recovery path, and working with its unnamed UPS vendor to understand and remediate the issues in the battery backup system.

Google's US East5 cloud region launched in 2022. The region – first announced in December 2021 and including three availability zones – was the second region in the Midwest and the 10th region in North America Google launched. In June 2024, the company announced plans to invest $2.3 billion into its Ohio data center campuses, adding to the $4.4bn already spent in the state since 2019.

Google experienced a power failure at its europe-west3-c zone in its cloud region in Frankfurt, Germany, in late 2024. That outage took more than 12 hours to resolve.