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What are data centres

Our love affair with the Cloud continues to grow.

According to a recent report by Gartner, the worldwide public Cloud services market is projected to grow 17.3% in 2019 to 206.2 billion dollars. The fastest growing section of the market is “Infrastructure as a Service” (or IaaS), which is expected to grow 26.7% from 2018, with revenue increasing from 31 to 39.5 Billion dollars.

We’re all on board.

It’s fair to assume that most Organisations use one or more Cloud-based platforms and/or services in some capacity, and with good reason.

Many Businesses have taken the decision to completely replace their outdated on-premise IT Systems with cost-effective and highly efficient Cloud-based alternatives because of the Commercial and Financial advantages of adopting Cloud-based services. The above statistics from Gartner provide a clear indication that this trend is set to continue throughout 2019 and beyond.

Data Centres are at the heart of Cloud services growth.

Data Centres are dedicated buildings that contain multiple servers. These servers host data, platforms and services, which are accessible through the internet. A typical Data Centre facility is safeguarded 24/7/365 and has multi-level security in place to prevent unauthorised access to the infrastructure.

No two data centres are the same.

In the mid-1990s, a Tiered Classification system for Data Centres was created by an Organisation called the Uptime Institute. This 4-tier classification system has become the global standard for identifying the complexity and redundancy of a data centres critical infrastructure by comparing data facilities and bench marking system availability.

Here’s a breakdown of the different types of Data Centre Tiers.

The following 4-tiered classification system from the Up-time Institute provides a benchmark for classifying system availability and comparing facilities.

Tier 1 data centre

What is a Tier 1 Data Centre?

A Tier 1 data centre has basic capacity. Tier-1 data centres are typically considered to be the least reliable ‘Entry point’ data centres because there is no redundancy and backup components in place. Because of this, there is a high risk of your systems going offline in the event of a power outage if you host your IT Systems in a Tier 1 Data Centre. It is also likely that you will experience downtime in the event of scheduled maintenance.

Despite this, Tier-1 data centres still typically feature an uninterruptible power supply to filter power spikes and outages, dedicated cooling equipment and an engine generator to protect the IT functions against extended power outages.


  • The cheapest entry point into Data Centre capability


  • Tier 1 Data Centres are non-redundant, which means they have the lowest up-time guarantee
  • You can expect service disruption in the event of a power outage
  • Any planned maintenance will result in downtime because of a lack of redundancy in place, although you will be informed in advance of any scheduled maintenance

Tier 2 data centre

What is a Tier 2 Data Centre?

A Tier 2 Data Centre is typically more reliable than a Tier 1 Data Centre because it incorporates additional backup and redundancy capacity components. Tier 2 status is awarded to Data Centres once they have met the Tier 1 criteria, in addition to offering partial redundancy through additional capacity components.

Partial redundancy.

Tier 2 Data Centres will typically feature redundant critical power and cooling components that allow planned service outages to be performed without effecting equipment up-time. Redundancy capacity components also provide an increased level of protection from equipment failure and IT process disruptions. Typical redundancy components that you’ll find in a Tier 2 Data Centre include additional power cooling equipment, Uninterruptible Power Supplies (UPS), Air Conditioning Units and engine generators.


  • Incorporates all tier-1 requirements, in addition to added levels of backup and redundancy
  • A longer up-time guarantee – Thanks to enhanced redundancy, planned outages will not affect equipment up-time
  • A cheaper way to guarantee redundancy without paying Tier-3 tier-4 costs


  • Lower up-time guarantees when compared to Tier 3 and Tier 4 data centres
  • Downtime will still be incurred during scheduled maintenance and when repair work is required
  • Unplanned outages will still potentially cause service disruption because the site doesn’t offer redundancy for every component

Tier 3 data centre

What is a Tier 3 Data Centre?

Tier 3 Data Centres are the most commonly used and cost-effective facilities for SMEs because of their strong up-time guarantee. On average, they are only expected to incur two hours annual downtime.

Tier 3 Data Centres are concurrently maintainable.

This means that every hardware component in the Data Centre can be taken offline for repair or scheduled maintenance without impacting the IT Operation, although unexpected failures and errors can still cause outages.


In addition to the critical component redundancy featured in tier-2 data centres, Tier 3 Data Centres incorporate dual-powered equipment, also known as “N+1”. This provides multiple paths for power and cooling outage protection. Some fault-resistant equipment may also be used in Tier 3 data centres. In this instance, these Data Centres are known as ‘Tier 3+’.


  • A cost-effective alternative to Tier-4 Data Centre facilities
  • The most cost-effective up-time guarantees
  • Any planned outages will not affect up-time
  • Any unplanned outages are unlikely to cause service disruption


  • Tier 3 redundancy doesn’t offer the high availability exclusive to Tier-4 Data Centres because not all equipment is fault resistant

Tier 4 data centre

What is a Tier 4 Data Centre?

Tier 4 Data Centres are Fault tolerant and have no single points of failure. They feature redundancy for every component. With a Tier 4 Data Centre, you can expect a service up-time of 99.99%, but this comes at a cost. Tier 4 Data Centre facilities are considerably more expensive than the preceding tiers.

In a Tier-4 Data Centre all essential equipment is physically copied, plus there is an additional backup generator. Also known as 2N+, this level of redundancy ensures that if any individual equipment fails or any interruptions occur, then these events will not affect the IT operations.

In addition.

Tier 4 Data Centres typically feature heightened levels of security (as do some Tier-3 data centres) including compartmentalised security zones that feature biometric access.


  • Tier 4 Data Centres offer the highest level of availability (99.99%)
  • It’s highly unlikely that either planned and unplanned outages will cause any disruption
  • Redundancy in place for every component
  • Any scheduled maintenance will not impact up-time


  • Tier 4 Data Centres are much more expensive than the preceding tiers
  • Many consider Tier 3 Data Centres to be the better option because they are cheaper, but the availability gap isn’t as wide

Why should you care about different Data Centre tiers?

Many Business that are moving to the Cloud will use platforms and services that are already hosted at a Data Centre. Because of this, its unlikely that you’ll ever need to know (or care) about the different levels of Tiered certification!


If you intend to deploy your data, systems and services in a Data Centre, then It’s important to understand your Business requirements before selecting a specific tier.

For example.

If you are a start-up or a Small Business that doesn’t require access to your data or applications 24/7/365, then then a Tier 1 or Tier 2 Data centre may prove to be enough for your requirements, just expect very occasional downtime to occur at evenings and weekends for planned maintenance.


If you run a Business that works around the clock then would be wise to host your critical applications and data at either a Tier 3 or Tier 4 data centre that has added layers of redundancy to safeguard against unexpected downtime and ensure that do downtime occurs during scheduled maintenance.

Thank you for reading our article!

We hope that you enjoyed this article ‘What are Data Centre Tiers and why should you care?’ OhSo Technical is a Professional IT Services Organisation that is based in Highams Park, London. In addition to our Fully Managed Services, we also provide a comprehensive range of Cloud Computing services and solutions. Our services include Cloud Strategy and Adoption consultancy, Office 365 Business implementation, Microsoft Azure services and Amazon Web Services.

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Being honest, we’re geeks, not writers. If you spot a mistake, or if you think something in this article is factually incorrect then we’d appreciate you dropping us a message to let us know. We’ll pay you back with our eternal gratitude!

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