Data center tiers are defined levels of resiliency andredundancy for IT facility infrastructure. They are widely used in thedata center,ISP andcloud computing industries as part of the engineering design forhigh availability systems. The data center tier system was created by theUptime Institute.[1]
The standard data center tiers are:[2]
A Tier III system is intended to operate at Tier II resiliency even when under maintenance, and a Tier IV system is intended to operate at Tier III resiliency even when under maintenance.
Most commercial data centers are Tier III; instead of using Tier IV datacentres, many large service providers typically use multipleavailability zones to implement of their services, thus achieving greater resilience than would be possible with any single data centre.[citation needed]
| Tier | Uptime guarantee per year | Downtime per year | Component redundancy |
|---|---|---|---|
| Tier 4 | 99.995% | <26.3 minutes | Fault tolerant (2N or 2N+1) |
| Tier 3 | 99.982% | <1.6 hours | Full N+1 |
| Tier 2 | 99.741% | <22 hours | Partial power and cooling redundancy (partial N+1) |
| Tier 1 | 99.671% | <28.8 hours | None |
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