📈 Continuous Availability Tiers

Tier classifications define data center resilience levels.

TIER I

• Small businesses
• Single path for power and cooling
• No redundancy
• Availability: 99.671% – 99.749%
• Downtime: 22.7–28.8 hours/year

TIER II

• Medium-sized businesses
• Some redundancy in power/cooling
• Availability: 99.982%
• Downtime: ~1.6 hours/year

TIER III

• Larger enterprises
• Multiple power/cooling paths (N+1)
• Fault tolerant
• Sustains 72-hour power outage
• Availability: 99.995%
• Downtime: ~25 minutes/year

TIER IV

• Critical mission enterprises
• Independent utility paths (2N+1)
• Fully redundant systems
• Sustains 96-hour outage
• Availability: Implied “six nines”

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