The tier 4 data centers are considered the most robust and less prone to failures. Tier 4 data centers are designed to host mission critical servers and computer systems, with fully redundant subsystems (cooling, power, network links, storage etc) and compartmentalized security zones controlled by biometric access control methods.

• 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.

Data Center Availability According To Tiers

The tier levels also describe the  uptime availability of data from the hardware at a location as follows:

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