The Definitive Guide toAI Data Centers
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Guide › Glossary › Tier IV

Tier IV

The top Uptime classification meaning fault tolerant: the facility survives any single failure with no impact.

Current numbers

Tier III / IV outcomesUptime Tier III concurrent-maintainability and Tier IV fault-tolerance outcomes under the standard's defined conditionsas of 2025 · register ↗
~25–40% facilitySavills May 2024 quoted whole-facility Tier IV-over-III cost estimate; price the required topology and test its paths separatelyas of 2024-05 · register ↗

Related terms: Fault tolerance

Where the guide uses this

12.2
The AI-Cluster Reliability Rethink: Goodput vs Facility Availability
12.4
SLAs, Goodput Contracts & Availability Commitments
12.1
Resilience Standards, Redundancy Topologies & Fault-Domain Engineering
0.4
The Standards & Specifications Landscape (Living Index)
13.1
Commissioning Fundamentals, Levels & Program Governance
0.5
Reliability, Redundancy & Availability: The Design-Basis Primer

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