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Data Centres (DC) are divided into 4 categories – Tier 1, Tier 2, Tier 3 and Tier 4 (Tier 4 – the highest category). Data Centres fall into specific categories on the basis of the reservation level of the technologies installed, physical security solutions, and building and site characteristics. Uptime Institute or TIA (Telecommunications Industry Association) approve official adequacy for a specific category.

Tier1 Tier2
Active equipment
N N+1 N+1 2N
Distribution ways 1 1 2 2
Concurrently maintainable NO NO YES YES
Annual downtime, h 28,8 22 1,6 0,4
Availability, % 99,671 99,749 99,982 99,995
Probability of discontinuance per 5 years, % 37,17 31,37 25,91 2,14

Tier 1: basic server room

Tier 2: duplication of active equipment N+1

The Data Centre matching the Tier 1 level has no duplicating active components or distribution ways. Scheduled works can only be carried out when the Data Centre is stopped. All system failures and failures of any part of the chain have influence on the server functioning.

The Data Centre has redundant components of active equipment (UPS, cooling mechanisms, network equipment) and only one distribution way. For the reasons mentioned above, the Data Centre has to be stopped during preventive works.

Tier 3: concurrently maintainable

Tier 4: dual infrastructure

Active equipment is duplicated on the N+1 principle. Distribution ways are duplicated – dual cooling piping, dual network connection, dual electrical installation. The Data Centre does not need to be stopped during preventive works. The centre is settled in the dedicated building, the site is enclosed.

Both active equipment and distribution paths are dual. The Data Centre withstands any unplanned failures. There are no Tier 4 Data Centres for commercial use in the Baltic States. It is commonly built as a large corporation or state data centre in a dedicated building.

The most popular Data Centres for commercial use are Tier 2 and Tier 3. Tier 1 has no reservation level, and Tier 4 is a private Data Centre most often. In addition to reservation level and availability, Tier 2 and Tier 3 Data Centres differ from each other in the site, building and other characteristics.

CharacteristicsTier 2 Tier 3
Duplicated network connection premises distanced by at least 20 metres NO YES
Duplicated network connection to the client‘s IT equipment NO YES
Minimal distance from railway or highway – 0.8 km, from airport or water body – 0.4 km NO
Minimal distance from public zone – 9.8 metres NO
By at least 9,1 metres separated parking for the staff and visitors NO
Separate driveway to the site for the staff and visitors NO
Dedicated building NO
Physically separated installation, unpacking and security premises NO
Server rooms are isolated from other rooms with walls resistant to fire for not less than 1 hour NO