Datacenter Tiers what does it all mean?

Datacenter Tiers are simply a method of rating data centers which has be recognised by the data center industry for measuring infrastructure standards. I won’t be going into the history of how these standards were developed or what a data center needs to do in order to qualify for each tier.

All you really need to understand is that all hardware can fail and if a server is placed within a data center at a particular tier you could have X amount of unavailability of that server due to failure of the data centers equipment.


Tier Level


Possible unavailability in a given year


Single non-redundant distribution path serving the IT equipment Non-redundant capacity components Basic site infrastructure with expected availability of 99.671%

1729.224 minutes



Meets or exceeds all Tier 1 requirements Redundant site infrastructure capacity components with expected availability of 99.741%

1361.304 minutes



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 with expected availability of 99.982%

94.608 minutes



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 with expected availability of 99.995%

26.28 minutes


One item we haven’t mentioned above is security, usually the higher the tier the more security measures have been put in place to prevent unauthorised access both physically and electronically.

Please also note that just because a company hosts their equipment in a tier 34 data centre it has no bearing on the quality or resiliency of the equipment they employ, nor does it mean they know how to implement a secure and resilient network.

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