Tier I
Single path for power and cooling distribution, no redundant components, 99.671% availability.
Tier II
Single path for power and cooling distribution, redundant components, 99.741% availability.
Tier III
Multiple power and cooling distribution paths, but only one path active, redundant components, concurrently maintainable, 99.982% availability.
Tier IV
Multiple active power and cooling distribution paths, redundant components, fault tolerant, 99.995% availability.