In the context of data centers, the terms "Tier 1", "Tier 2", "Tier 3", and "Tier 4" refer to different levels of infrastructure reliability and fault tolerance. These tiers are defined by the Uptime Institute, a leading organization that provides independent guidance and certification for data center design, construction, and operations.
The Uptime Institute's Tier Classification System is a standardized framework that provides a consistent way to describe the reliability and fault tolerance of data center infrastructure. The tiers are defined as follows:
Tier 2: Redundant capacity components
Tier 2 data centers are designed to provide redundant capacity components, but do not have redundant sites. These data centers typically have multiple power and cooling sources, as well as redundant distribution paths serving the IT equipment. Tier 2 data centers are generally used for applications that require higher levels of availability than Tier 1, but do not require the highest levels of fault tolerance.
Tier 3: Concurrently maintainable
Tier 3 data centers are designed to be concurrently maintainable, with redundant and diverse components. These data centers typically have redundant power and cooling sources, as well as multiple distribution paths serving the IT equipment. Tier 3 data centers are generally used for mission-critical applications that require high levels of availability and fault tolerance.
Tier 4: Fault-tolerant