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Physical Infrastructure

N+1 Redundancy

Design model where one additional unit is deployed beyond the minimum required, so the system survives any single failure.

Full Definition

N+1 redundancy means deploying one more unit than the minimum required (N) so that if any single unit fails, the remaining N units maintain full service. Common in data centre UPS, cooling, and generator design. For example, if 3 CRAC units are needed (N=3), 4 are installed (3+1). 2N redundancy duplicates the entire system (two separate power paths, two cooling loops) for higher resilience. N+1 is standard for Tier III; 2N is typical for Tier IV.

Also Known As

n+1n plus 1redundancy2n redundancy

Source Reference

Uptime Institute — Tier Standard: Topology (2022)

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