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Driving Innovation

Data Center Construction

Data Center Tiers Explained

If your organization is considering building a data center, determine the proper facility tier classification standard to follow based on the desired level of facility performance and availability.

Data facility classification standards were implemented by the Uptime Institute, which is a leading third-party data center research, education, and consulting organization. The Uptime Institute focuses on data center performance and efficiency and its Tier Standard Classifications are recognized as the industry’s most trusted global standard for data facility reliability and overall performance.

The Tier Standard Classifications allow for various levels of performance to be chosen based on the intended applications and business parameters associated with those applications. Tier Standard Classifications were created to describe the infrastructure required to sustain data facility operations. All subsystems and systems must be consistently deployed with the same facility uptime objective to satisfy the unique tier requirements. Therefore, the tier rating for an entire data facility is limited by the rating of the weakest subsystem that impacts facility operations.

The four Tier Standard Classifications as defined by the Uptime Institute include:

  • Tier I – Basic Site Infrastructure – Composed of a single path for power and cooling distribution, without redundant components, providing 99.671% availability. Includes: a dedicated space for IT Systems; a UPS to filter power spikes and momentary outages; dedicated cooling equipment, and on-site power production (ie engine generator, fuel cell) to protect IT functions from extended power outages.
  • Tier II – Redundant Site Infrastructure Components – Composed of a single path for power and cooling distribution, with redundant components, providing 99.741% availability. The redundant components are: extra on-site power production (ie engine generator, fuel cell), UPS modules and energy storage, chillers, heat rejection equipment, pumps, cooling units, and fuel tanks.
  • Tier III – Concurrently Maintainable Site Infrastructure – Composed of multiple, independent power and cooling distribution paths with one path active and one alternate path, has redundant components and is concurrently maintainable, providing 99.982% availability.
  • Tier IV – Fault Tolerant Site Infrastructure – Composed of multiple active power and cooling distribution paths, has redundant components, and is fault tolerant, providing 99.995% availability.

Want to know where the most significant deviations from the Tier Standard Classifications occur? Read our article: Data Facility Tier Standard Classifications – Frequent Non-Compliance Trends

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Data Center Tier Requirements Summary
Tier I Tier II Tier III Tier IV
Minimum Capacity Components to Support the IT Load N N + 1 N + 1 N
After any failure
Distribution Paths - Electrical Power Backbone 1 1 1 Active + 1 Alternate 2 Simultaneously Active
Critical Power Distribution 1 1 2 Simultaneously Active 2 Simultaneously Active
Concurrently Maintainable No No Yes Yes
Fault Tolerance No No No Yes
Compartmentalization No No No Yes
Continuous Cooling No No No Yes





Source: Uptime Institute®, a division of The 451 Group. "Data Center Site Infrastructure Tier Standard: Topology©" Uptime Institute, www.uptimeinstitute.com/resources/asset/tier-standard-topology. Accessed 11 December, 2019