What is TIER III?

TIER III is a data center classification level defined by the Uptime Institute, ensuring a concurrently maintainable infrastructure: the ability to service and replace any component without interrupting IT operations.

A TIER III data center requires redundancy of all key subsystems (power, cooling, etc.) based on an N+1 configuration. Backup diesel generators must provide sufficient runtime for autonomous operation of the facility, with adequate fuel reserves and the capability for refueling without downtime. This enables planned maintenance activities to be performed without service interruption. At the same time, the facility remains vulnerable to certain types of failures and incidents (such as critical equipment failure or operator error). The expected annual availability of a TIER III data center is 99.982%, corresponding to no more than 1.6 hours (1 hour 36 minutes) of downtime per year. Certification is validated through a review of design documentation and an inspection of the constructed facility by the Uptime Institute.