Data centre tier classification

To test the availability of a data centre, the American standard TIA-942 was drawn up for the Uptime Institute in 2005. It classifies data centres in four levels: Tier 1 (Basic capacity), Tier 2 (Redundancy or Major components), Tier 3 (Concurrently maintainable) and Tier 4 (Fault tolerant). The data centre tier numbers indicate the guarantees and redundancy. The higher the classification, the better the availability of the data centre. Each tier (layer) builds on the previous layer; tier 4 contains all components of tier 1, 2 and 3 plus a number of additional requirements.

The four tiers

Tier 1

This is the simplest implementation and the basis that every data centre must meet. There is one energy supplier, one UPS (uninterruptible power supply) and one power supply to the components (CRVK-1). There is no redundancy. If there is a planned or unplanned outage then this leads to downtime.

Tier 2

Tier 2 is slightly more extensive. This involves one energy supplier, one NSA (emergency power generator), one USP and one power supply to the components. The NSA can be implemented in the event of a power failure. However, not all parts are redundant, so downtime is still present during maintenance or downtime.

Tier 3

In tier 3 there is redundancy of the installations and components. There are two energy suppliers, two NSAs, two UPSs and two power supplies to the components. Only one path is always active. In the event of maintenance or breakdown, the other path becomes active and does not affect availability.

Tier 4

In tier 4, there is full redundancy. There are two energy suppliers, two NSAs, two UPSs and two power supplies to the components. The big difference with tier 3 is that in tier 4 both paths provide half of the power. In case of failure or maintenance, the other path will provide the total power.

Tier classification at Dutch data centres

The data centre tier classification is based on American standards. Dutch data centres have been set up slightly differently, which is why the classification is more difficult. Tier 1 and Tier 2 are easy to achieve. 99.99% availability is possible in the Netherlands, so tier 3 data centres are also available here (Fundaments works from these). Tier 4 data centres are not available in the Netherlands. In tier 4, power supply must be delivered via two completely separate paths. In the Netherlands we have one infrastructure for the steam network, which means that the Tier 4 classification is not possible here.

Tier 1Tier 2Tier 3Tier 4
Downtime/year28,8 hours22 hours1,6 hours0,8 hours
Power infrastructure1111+1
Power source111+11+1

Fundaments only works with certified Dutch Tier 3 data centres. This guarantees the quality and availability we can deliver. Would you like to know more about Fundaments services and the data centres from which we operate? Please feel free to contact us on 088 4227 227 or email us at

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