The below table gives a quick overview of Datacenter Qualification and what are the requirements for each of the different tiers

 

Tier level


Requirements

1

  • Single non-redundant distribution path serving the IT equipment
  • Non-redundant capacity components
  • Basic site infrastructure guaranteeing 99.671% availability

2

  • Meets or exceeds all Tier 1 requirements
  • Redundant site infrastructure capacity components guaranteeing 99.741% availability

3

  • Meets or exceeds all Tier 1 and Tier 2 requirements
  • Multiple independent distribution paths serving the IT equipment
  • All IT equipment must be dual-powered and fully compatible with the topology of a site's architecture
  • Concurrently maintainable site infrastructure guaranteeing 99.982% availability

4

  • Meets or exceeds all Tier 1, Tier 2 and Tier 3 requirements
  • All cooling equipment is independently dual-powered, including chillers and heating, ventilating and air-conditioning (HVAC) systems
  • Fault-tolerant site infrastructure with electrical power storage and distribution facilities guaranteeing 99.995% availability

 

Please be aware that there are only a few classified Tier4 Datacenter out there.