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Introduction to Data Center Tiers

Data centre tier levels can be confusing when looking for an IT infrastructure solution for your business. Simply put, these tiers are a method used to describe and evaluate the service offering and infrastructure of a data centre, in relation to business requirements. They are generally consistent across the data centre industry, even if the designs of the data centres themselves are unique - the classification system focuses instead on performance, uptime and redundancy measures. This allows businesses to choose an ideal data centre solution based on their requirements for their technology infrastructure and service level.

Data centre tiers were first introduced by the Telecoms Industry Association, with an updated version released by the Uptime Institute. These are the most widely used across the industry and comprise of 4 different levels: Tier 1 through 4. The specifications for each tier are progressive, which means that a data centre that fulfils Tier 2, will fulfil all the requirements of Tier 1, plus those of Tier 2.

For example:

Tier 4 = Tier 3 + Tier 2 + Tier 1

Overview of a Tier 1 Data Center

Typical uptime: 99.6+%

Tier 1 data centres have been derisively referred to as ‘warehouses with power’, as the investment in these are usually driven by cost and time to market. They tend to be tactical choices for businesses that need support that fits in their budget or for businesses that don’t rely on real-time service outputs. They are designed with a single input for power and for cooling, with little to no provisions for redundancies or outages.

Overview of a Tier 2 Data Centre

Typical uptime: 99.7+%

A Tier 2 data centre is very similar to a Tier 1 centre, as they typically have one path for power and cooling. However, Tier 2 data centres do account for redundancies with extra equipment on site; but these tend to be kept separately from main equipment and only used in the case of a total outage.

Overview of a Tier 3 Data Center

Typical uptime: 99.98+%

Data centres classified as Tier 3 are the most common type used by businesses all over the world. Tier 3 data centre requirements include all of the prior tiers but add a layer of reliability and long-term viability for businesses looking for year on year support. Businesses use Tier 3 centres as strategic assets, as the infrastructures they form part of are built beyond their current IT requirements. With rigorous uptime requirements, they are designed with multiple paths for cooling and power. Measures for multiple redundancies are in place with additional equipment taking power and network connection from independent entries, allowing for concurrent availability.

Overview of a Tier 4 Data Center

Typical uptime: 99.99+%

Tier 4 is the highest possible classification for a data centre and typically costs twice as much to build as a Tier 3 centre. This is because every piece of equipment in the facility has a backup powered independently, with a seamless transition in case of a failure. This calibre of data centre is built to have no single point of failure, with multiple power and cooling paths into equipment and more than one connection to the main power grid. This tier of data centre is not generally as common as the other tiers, and businesses tend to choose Tier 3 options over the increased cost of a Tier 4. A proactively maintained and tested Tier 3 data centre infrastructure will serve most businesses better than a single Tier 4 data centre. The phenomenon of data gravity (where data attracts data) means that optimising data storage across facilities holds less risk than consolidating everything into a Tier 4 centre.


Data centres can be a useful framework for aligning your business requirements with a potential data centre provider. When researching for enterprise IT solutions, it is imperative to ask the right questions, talk to the team running the facility to find out what kind of testing and monitoring they do routinely. Tier 3 fits the requirements for most businesses, with a balance between service and resource outlay. A strategic solution often splits requirements across multiple Tier 3 centres, giving your business a higher uptime than one poorly run Tier 4 data centre. Our Tier 3 data centre campus on Hanbury Street has three separate facilities, with multiple fibre entries and redundancies, giving your business the ideal technology platform to grow. We act as your strategic partner, enabling access to diverse connected communities of interest, all within our data centres in the heart of the City of London.