Rating/Tier* Level
ANSI/TIA-942 describes four Rating/Tier* levels in which data centers can be classified. Below is the high level description of each Rating/Tier* level. Detailed specifications are given in the ANSI/TIA-942 standard.
Rated-1/Tier-1*: Basic Site Infrastructure
A data center which has single capacity components and a single, non-redundant distribution path serving the computer equipment. It has limited protection against physical events.
Rated-2/Tier-2*: Redundant Capacity Component Site Infrastructure
A data center which has redundant capacity components and a single, non-redundant distribution path serving the computer equipment. It has improved protection against physical events.
Rated-3/Tier-3*: Concurrently Maintainable Site Infrastructure
A data center which has redundant capacity components and multiple independent distribution paths serving the computer equipment. Typically, only one distribution path serves the computer equipment at any time. The site is concurrently maintainable which means that each and every capacity component including elements which are part of the distribution path, can be removed/replaced/serviced on a planned basis without disrupting the ICT capabilities to the End-User. It has protection against most physical events.
Rated-4/Tier-4*: Fault Tolerant Site Infrastructure
A data center which has redundant capacity components and multiple independent distribution paths serving the computer equipment which all are active. The data center allows concurrent maintainability and one (1) fault anywhere in the installation without causing downtime. It has protection against almost all physical events.
Validity
TIA-942 standard certification is valid for 3 years. By the end of year-1 and year-2, the data center should undergo a surveillance audit. By the end of year-3, the data center has to undergo a recertification audit in order to keep its certification valid.
* The term ‘Tier’ was used in the ANSI/TIA-942 Standard until the ANSI/TIA-942:March-2014 edition. In the March 2014 edition the term ‘Tier’ has been replaced by either ‘Rated’ or ‘Rating’.