The demand for proven high availability and redundancy in the data center is growing as more corporations are moving toward an outsourced model. Running mission critical applications and production systems from third party data centers allows IT leaders to reduce costs and sleep easy at night knowing their systems are protected and running 24/7/365.

Trusting your equipment and operations are in safe hands means believing that the site infrastructure and fault tolerance of the colocation provider is as solid as they say it is. Ask what classification their data center maintains and understand what the different classifications mean.

In 1995, Uptime Institute developed a Tier system for classifying data centers and outlining standards for site infrastructure requirements. A Tier 1-4 rating is given to data centers based on review of design topology and site sustainability.

Colocation providers and data center managers can loosely determine the classification of their site by examining the following standards:

Tier I – Non-redundant capacity components and single non-redundant path distribution paths serving the site’s computer equipment (basically a server room).

Tier II – Redundant capacity components and single non-redundant distribution paths serving the site’s computer equipment, guaranteeing 99.741% availability.

Tier III – Redundant capacity components and multiple distribution paths serving the site’s computer equipment. Generally, only one distribution path serves the computer equipment at any time. Tier III facilities are concurrently maintainable with all IT equipment being dual-powered and fully compatible with the topology of a site’s architecture.

Tier IV – Redundant capacity systems and multiple distribution paths simultaneously serving the site’s computer equipment. 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.

Classifications are officially determined by review of the data center by UT certified personnel.


  1. Your add for a consulting firm does not make it the truth! There have been several data center tier systems all created and promoted by various consulting firms (of which the Uptime Institute is one). Each of them have proprietary standards not vetted by any peer group and not publicly available. That is the TRUTH about tier classifications!

    1. Thanks for your comments, Gene. My intention was not to give adspace for the Uptime Institute, but to discuss a baseline for evaluating a data center or colocation provider. FIBERTOWN is not directly affiliated with UT, except to point out that its Tier descriptions are widely used. We do not limit our standards to those only prescribed by UT.

  2. Good overview of the Uptime Tier classifications. I believe that this classification is still the best method available to understand what you are getting in your colocation facility. Unfortunately numerous colocation providers embelish their tier classification without any real substance behind it. If you are a buyer of colocation have your colocation provider prove that they actually have the redundancies needed to support their tier claim. Caveat emptor.

  3. Hi Gene! Uptime is a private consulting company, you are right. And most well known consulting companies are just packing bullshit providers – I completely agree with you again.
    But the difference, at least from my point of view, is that Tiers from Uptime are completely open and ever major papers are free.
    Will you be so kind to note some other comparable choice for this industry? I cant for my shame.

  4. Basing a decision on a 4 level model makes no sense. Some companies claim they are a 2+ in fact there is no such rating you are either a 2 or a 3. This has a lot of unfair impact if you are selling a company. The Gartner maturity models typically use at least 7 levels so you get a granular view that is a lot more accurate. UI introduced something good it just needs to get better.

  5. Hi Warhawk! I am sorry, but from my point of view, Gartner is in the list of consulting companies mentioned me before. Quite comprehensive CMM by Carnegie Mellon University has also only four levels – this is quite enough to make choice.

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