What are data centre tiers?

Tiers I through IV rate how redundant a data centre is - how many things can break before your servers go offline. Tier I (99.671% uptime) has no redundancy - any maintenance requires a full shutdown. Tier II (99.741%) adds redundant UPS and generators but a single distribution path. Tier III (99.982%) has multiple distribution paths allowing any component to be maintained without downtime - this is the standard for commercial colocation. Tier IV (99.995%) is fully fault-tolerant with simultaneously active dual paths, meaning any single failure has zero impact on operations. Construction costs increase roughly 30-50% per tier level, from $6-8M/MW for Tier I to $16-22M/MW for Tier IV.