Data centre tiers

Data centre tiers are defined levels of resiliency and redundancy for IT facility infrastructure. They are widely used in the data center, ISP and cloud computing industries as part of the engineering design for high availability systems.

The standard data center tiers are:

A Tier III system is intended to operate at Tier II resiliency even when under maintenance; a Tier IV system is intended to operate at Tier III resiliency even when under maintenance.
 * Tier I: no redundancy
 * Tier II: partial N+1 redundancy
 * Tier III: full N+1 redundancy of all systems, including power supply and cooling distribution paths
 * Tier IV: as Tier III, but with 2N+1 redundancy of all systems

Most commercial data centers are Tier III; large service providers typically use multiple availability zones to implement resilience of their services.

The data center tier system was created by the Uptime Institute.