Tier 1: Guaranteeing 99.671% availability
Tier 2: Guaranteeing 99.741% availability
Tier 3: Guaranteeing 99.982% availability
Tier 4: Guaranteeing 99.995% availability

Tier 1 = Non-redundant capacity components (single uplink and servers).
Tier 2 = Tier 1 + Redundant capacity components.
Tier 3 = Tier 1 + Tier 2 + Dual-powered equipments and multiple uplinks.
Tier 4 = Tier 1 + Tier 2 + Tier 3 + all components are fully fault-tolerant including uplinks, storage, chillers, HVAC systems, servers etc. Everything is dual-powered.