Data center standards exist to evaluate the quality and reliability of a data center’s server hosting ability. The Uptime Institute uses a somewhat mysterious four-tier ranking system as a benchmark for determining the reliability of a data center. This proprietary rating system begins with Tier I data centers, which are basically warehouses with power, and ends with Tier IV data centers, which offer 2N redundant power and cooling in addition to a 99.99% uptime guarantee.







A Tier III data center is concurrently maintainable, allowing for any planned maintenance activity of power and cooling systems to take place without disrupting the operation of computer hardware located in the data center. In terms of redundancy, Tier III offers N+1 availability. Any unplanned activity such as operational errors or spontaneous failures of infrastructure components can still cause an outage. In other words, Tier III isn’t completely fault tolerant. A Tier 4 data center is fault-tolerant, allowing for the occurrence of any unplanned activity while still maintaining operations. Tier 4 facilities have no single points of failure.


1Non-redundant capacity components (single uplink and servers).99.671%
2Tier 1 + Redundant capacity components.99.741%
3Tier 1 + Tier 2 + Dual-powered equipments and multiple uplinks.99.982%
4Tier 1 + Tier 2 + Tier 3 + all components are fully fault-tolerant including uplinks, storage, chillers, HVAC systems, servers etc. Everything is dual-powered.99.995%