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What Are Data Center Tiers?

Data center 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 center, in relation to business requirements. They are generally consistent across the data center industry, even if the designs of the data centers themselves are unique - the classification system focuses instead on performance, uptime, and redundancy measures. This allows businesses to choose an ideal data center solution based on their requirements for their technology infrastructure and service level.

Data center tiers: Definition explained

Data center 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 four levels: Tiers 1 through 4. The specifications for each tier are progressive, which means that a data center that fulfills Tier 2 will fulfill all the requirements of Tier 1, plus those of Tier 2.

For example:

Tier 4 = Tier 3 + Tier 2 + Tier 1

Data center tiers: Classification standards

The following are the factors that are considered when setting data center tier standards:

  1. Availability, redundancy, and uptime: How long is this data center expected to function annually, and what steps are in place to minimize downtime?

  2. Efficiency and sustainability: How efficiently does the data center utilize its resources, and what is its anticipated lifespan in the face of emerging technologies?

  3. Cost: What are the operating expenses of the data center?

  4. Security: How is the data center safeguarding against data breaches and other risks?

Overview of a Tier 1 data center: Standards, requirements, and specifications

Typical uptime: 99.6+%

Tier 1 data centers have been derisively referred to as ‘warehouses with power’, as the investment in these is 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 cooling, with little to no provisions for redundancies or outages.

Overview of a Tier 2 data center: Standards, requirements, and specifications

Typical uptime: 99.7+%

A Tier 2 data center is very similar to a Tier 1 center, as they typically have one path for power and cooling. However, Tier 2 data centers 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: Standards, requirements, and specifications

Typical uptime: 99.98+%

Data centers classified as Tier 3 are the most common type used by businesses worldwide. Tier 3 data center 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 centers as strategic assets, as 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: Standards, requirements, and specifications

Typical uptime: 99.99+%

Tier 4 is the highest possible classification for a data center and typically costs twice as much to build as a Tier 3 center. This is because every piece of equipment in the facility has a backup powered independently, with a seamless transition in case of failure. This caliber of data center 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 center 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 center infrastructure will serve most businesses better than a single Tier 4 data center. The phenomenon of Data Gravity (where data attracts data) means that optimizing data storage across facilities holds less risk than consolidating everything into a Tier 4 center.


Data centers can be a useful framework for aligning your business requirements with a potential data center 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 centers, giving your business a higher uptime than one poorly run Tier 4 data center.

Our Tier 3 data center campus on Hanbury Street has three separate facilities with multiple fiber 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 centers in the heart of the City of London.

Frequently Asked Questions (FAQs) About Data Center Tiers

What are the main standards for data centers?

The main standards for data centers are determined by The Uptime Institute's Tier system. This classification system provides a standardized way to measure a data center's level of resilience and availability.

What is the highest-tier data center?

The highest widely recognized tier data center classification is Tier 4. A Tier 4 data center is designed to be fully fault-tolerant, with redundant systems for all critical components. It offers the highest level of availability and has an uptime of 99.995%. It can withstand a wide range of potential disruptions and offers the most reliable infrastructure.

What is Tier 3 data center requirements?

Tier 3 data center requirements include redundant components for power and cooling, multiple independent distribution paths for power, and concurrent maintainability, allowing for planned maintenance without downtime. It should also have a minimum of N+1 redundancy for its critical systems.

What is Tier 4 data center criteria?

Tier 4 data center criteria include all the requirements of Tier 3, but with additional features like fault tolerance, which means there are no single points of failure in the infrastructure. It should have multiple active power and cooling distribution paths, as well as a fault-tolerant design for mechanical and electrical systems.

What is tier specification of data center?

The tier specification of a data center refers to its classification according to The Uptime Institute's Tier system, which evaluates its resilience and availability. The classification is based on specific criteria such as redundancy, concurrent maintainability, and fault tolerance. The higher the tier, the more reliable and available the data center.