Data centre tiers describe specific kinds of data centre infrastructure. Tier 1 is the simplest infrastructure, while Tier 4 is the most complex and has the most redundant components. Each tier includes the required components of all the tiers below it.
- Tier 1: A Tier 1 data centre has a single path for power and cooling and few, if any, redundant and backup components. It has an expected uptime of 99.671% (28.8 hours of downtime annually).
- Tier 2: A Tier 2 data centre has a single path for power and cooling and some redundant and backup components. It has an expected uptime of 99.741% (22 hours of downtime annually).
- Tier 3: A Tier 3 data centre has multiple paths for power and cooling and systems in place to update and maintain it without taking it offline. It has an expected uptime of 99.982% (1.6 hours of downtime annually).
- Tier 4: A Tier 4 data centre is built to be completely fault-tolerant and has redundancy for every component. It has an expected uptime of 99.995% (26.3 minutes of downtime annually).