Data Center Tiers: Why Do They Matter?

When dealing with Data Centers (DCs), it’s helpful to understand what Data Center tiers are and how they affect IT organizations. Here’s a brief overview of what a data center tier is, what they tell people about your data center, and why they’re valuable to have.

What are Data Center Tiers?

Data center tiers are a system created by Uptime Institute LLC to describe the availability of infrastructure resources in a facility. A division of 451 Group, the Uptime Institute is the standard for this certification effort, which defines what is required to ensure that data centers meet an organization’s business demands. The tiering system came into place in the mid-1990s, making choosing a data center design and construction, whether it be public or private, a lot easier when it comes to predicted uptime and availability.

There are four tiers, ranked by Roman numerals from Tier I – the most basic data center design meeting the Institute’s core requirements – to Tier IV – the most fault-tolerant and available data center design. Note that only Roman lettering is allowed; any data center advertising itself with Arabic numerals – Tier 3, for example – should be reviewed as it might not be certified by the Uptime Institute.

As the tier levels increase, organizations must make bigger investments to meet certification criteria. Organizations should prepare a risk assessment that balances business risk against cost and use this to decide which tier is right for them. The Uptime Institute has its own professional services group that can help organizations prepare such assessments and then provide help to design the facility.

data center tiers

Data Center Tier Level

Tier 1 (Basic Capacity)

Tier 1 goes beyond staging your servers in a spare office or large closet inside a larger facility. Tier 1 DCs need a dedicated space for all your IT systems (a server room which may or may not include a locked door); uninterruptable power supplies (UPSes) to condition incoming power and to prevent spikes from damaging your equipment; a controlled cooling control environment that runs 24x7x365; and a generator to keep your equipment running during an extended power outage.

Tier 2 (Redundant Capacity)

Tier 2 offers an infrastructure that is more redundant and better protected. The requirements include everything from tier 1 but with a backup system for redundancy. They still have the single path model for power and cooling but have some redundant components such as generators and backup cooling systems. This allows for a higher uptime of approximately 99.741% or 22 hours of downtime per year, but this tier doesn’t guarantee a completely redundant system for the best performance and reliability.

Tier 3 (Concurrently maintainable DC)

A tier 3 DC incorporates all the characteristics of tier 1 and tier 2. A tier 3 data center also requires that any power and cooling equipment servicing the DC can be shut down for maintenance without affecting your IT processing. All IT equipment must have dual power supplies attached to different UPS units, such that a UPS unit can be taken offline without crashing servers or cutting off network connectivity. Redundant cooling systems must also be in place so that if one cooling unit fails, the other one kicks in and continues to cool the room. Tier 3 DCs are not fault-tolerant as they may share different components such as utility company feeds and external cooling system components that reside outside the data center.

Tier 4 (Fault Tolerance)

A Tier 4 data center is built to be completely fault tolerant. It has several independent and physically isolated systems that act as redundant capacity components and distribution paths. The separation is necessary to prevent an event from compromising both systems. Tier 4 has an expected uptime of 99.995%, which means 26.3 minutes of downtime annually.

Tier 4 either have 2N or 2N+1 redundancy:

  • 2N (or N+N) redundancy means the facility has a wholly mirrored, independent system on standby. If anything happens to a primary component, an identical backup replica starts working to ensure continued operations.
  • The 2N+1 model provides twice the operational capacity (2N) and an additional backup component (+1) in case a failure happens while a secondary system is active.

When a piece of equipment fails, or there is an interruption in the distribution path, IT operations will not be affected. However, if the redundant components or distribution paths are shut down for maintenance, the environment may experience a higher risk of disruption if a failure occurs. That’s why a Tier 4 data center does not guarantee 100% uptime.

data center tiers

What are the benefits of having a Tier-Certified Data Center?

Official certification from Uptime Institute can increase credibility and trust with current and prospective customers. Uptime Institute has issued over 2,500 certifications across the world and continues to be recognized as a global standard for data center reliability and overall performance.

The main benefits of having a certified data center by Uptime Institute are that it:

  • Shows investors, clients, and the industry that your data center can meet the highest standards for IT functionality and capacity
  • Validates that your system design is consistent with your uptime objective
  • Ensures that your organization’s capital investments yield desired results
  • Shows that your company has action plans in place to minimize unplanned downtime and unnecessary spending
  • Prove to parties involved that your strategy is clearly defined and passes thorough assessments from industry experts

How to choose the right data center tier

As we have already seen, higher data center tiers typically offer a more reliable service. However, selecting a tier 3 or tier 4 data center does not always represent the right choice. Decision-makers should choose the data center tier that most closely fits their business requirements. Certain types of organizations will typically veer towards choosing specific tiers.

The following is a brief breakdown of each tier’s typical customers.

  • Tier 1: These data centers are typically best suited to very small businesses looking for the most affordable hosting option. Small companies without complex IT requirements or the need to deliver service 24×7 can tolerate more frequent downtime.
  • Tier 2: These facilities are a good option for SMBs that want a cost-effective option but one that nevertheless offers more reliability than tier 1. If an organization’s online services aren’t business critical and it can accommodate some downtime, then Tier 2 may meet its needs.
  • Tier 3: These types of data centers are favored by SMBs whose IT operations need additional fail-safes over those basic protections offered by the lower tiers but who are still looking for a cost-effective option. Businesses that host extensive data sets (especially customer data) are well-suited to this tier.
  • Tier 4: This type of data center is typically used by large, global businesses or public sector organizations that require uninterrupted availability. Organizations with mission-critical servers and intense customer or business demands would be well suited to a Tier 4 facility.

data center tiers


The points to be highlighted are the definition and benefits of Tier itself are set in a standard topology and focus on data center infrastructure. Tier data center adapts to business requirements, and each company certainly has different needs. This means data center Tier IV is not necessarily better than other Tiers.

Thus, the tier levels meanings for a data center classification. Along with the various scales the company needs to start using technology to improve its service efficiency, utilization of data centers is almost inevitable. It can bolster digital transformation and open new business opportunities for companies that use suitable data center services.


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