Datacenters, TIER levels
TIER I: Basic Data Center
It is a simple installation, which does not have redundant main components (air conditioning, electrical supply) and therefore will lose its operating capacity in the event of any failure.
It may or may not have raised floors, backup generators or UPS.
Likewise, maintenance operations will result in system downtime.
Availability of 99.671%. (1.729 minutes per year)
TIER II: Redundant Data Center
Data centers in this category have redundant cooling, but have a single electrical supply.
In this case, the floors are raised, it has auxiliary generators or UPS.
However, they are connected to a single electrical and cooling distribution line.
These are therefore installations with a certain degree of fault tolerance and which allow for some “online” maintenance operations.
Availability of 99.741%. (1.361 minutes per year)
TIER III: Concurrently Maintainable Data Center
These data centers have significant levels of fault tolerance by having all basic equipment redundant, including power supply and cooling. But only with one active.
All servers should have dual power (ideally) and in principle the Datacenter does not require shutdowns for basic maintenance operations.
As an additional note, it is also a requirement that you can upgrade to TIER IV without service interruption.
Availability of 99.982%. (94 minutes per year)
TIER IV: Fault-Tolerant Data Center
This is the most demanding classification, which involves meeting TIER III requirements as well as supporting failures in any of its components that disable a line (supply, cooling).
Connected to multiple electrical and cooling distribution lines and each with multiple redundant components.
Tier IV certification is an approval process that consists of 38 tough endurance tests for the equipment and the installation. One of these tests, for example, consists of nothing less than filling the server room with heaters at full power to test the building's ability to dissipate heat.
Availability of 99.995%. (26 minutes per year)
