How many tiers are there of data centers? | HCL Technologies

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How many tiers are there of data centers?

The Uptime Institute has defined four different tiers of data centers (this definition is most commonly used):

  • Tier I (99.67% availability) ~29 hours downtime in a year
  • Tier II (99.74% availability) ~23 hours downtime in a year
  • Tier III (99.98% availability) ~1.58 hours downtime in a year
  • Tier IV (99.995% availability) ~ 0.438 hours downtime in a year

In practice, Tier II and Tier III data centers are the most common.