The Uptime Institute created an industry-standard classification system for levels of site infrastructure functionality offered by different data centers. This system contains four data center tiers:
- Tier 1: Composed of a single path for power and cooling distribution, without redundant components, providing 99.671% availability.
- Tier II: Composed of a single path for power and cooling distribution, with redundant components, providing 99.741% availability.
- Tier III: Composed of multiple active power and cooling distribution paths, but only one path active, has redundant components, and is concurrently maintainable, providing 99.982% availability.
- Tier IV: Composed of multiple active power and cooling distribution paths, has redundant components, and is fault tolerant, providing 99.995% availability.
