If you have a data center where the entire infrastructure must be completely shutdown on an annual basis to perform preventative maintenance and repair work, what tier level would this represent?

Tier I, as defined by the Uptime Institute Tier Classification System, has a single non-redundant distribution path for power and cooling with no redundant capacity components. Because there is no way to isolate components while keeping the IT load running, all maintenance and repair work requires a planned full-facility shutdown. The requirement for an annual complete shutdown directly maps to this Tier I characteristic.

Tier II includes redundant capacity components such as UPS modules and generators, allowing some maintenance activities on those components without requiring a complete shutdown of the entire infrastructure.

Tier III is concurrently maintainable, meaning any single component in the power or cooling path can be taken offline for maintenance without shutting down the IT load, making a full annual shutdown unnecessary.

Tier IV is fault tolerant with fully redundant active power and cooling paths, capable of sustaining any single failure or maintenance event without any interruption to IT operations.