Data Center Tier Classification: Tier 1, Tier 2, Tier 3 vs Tier 4

What are data center tier classifications? Why do they matter? In this article, we will be discussing the different data center tier levels, why they matter and what to look for. Data center tier classifications apply to colocation hosting, dedicated servers and cloud infrastructure such as cloud servers and storage. It is important to know the difference between tier standards before making an investment in hosting services for your business.

Uptime Institute & 451 Group

First off, the Uptime Institute is the de facto source for standardizing what it means to have a Tier 1, Tier 2, Tier 3 or Tier 4 data center facility. The Uptime Institute was founded in 1993 and the first to pioneer an end-user community and proprietary certifications focused on improving the reliability and uninterruptible availability in data centers and IT organizations. Uptime Institute was later acquired by 451 Group, a technology analyst company focusing on research and knowledge related to the IT industry. 451 Group provides thought leadership, syndicated research, and professional services for the entire IT ecosystem covering facilities, hardware, and software.

Data center tier classification explained

As mentioned previously, the Uptime Institute classifies and certifies both public and private data center facilities based on four different tier levels – Tier 1, Tier 2, Tier 3 and Tier 4. Each tier level represents a different level of data center availability based on redundant systems and processes. Why is this important? With different tier levels and availability, buyers can anticipate the amount of downtime or interruption per year. It could be less than an hour or as much as days of interruption.

It is important to note that not all data centers go through the Uptime Institute certification process. It can be very expensive, resource and time intensive. Therefore, you may see ratings such as Uptime Institute Tier III for some data center facilities or you may see a data center post that they meet or exceed all standards for a Tier III certified data center. Make sure to ask potential data centers for certification and compliance documents that are important to you. Many times, you can find this on their website.

Tier I data center

This is the lowest certification awarded by the Uptime Institute. When you see Tier 1, I want you to think of an older building, telecom carrier point of presence (PoP), office building or something to that extent.

Tier 1 data centers represent 99.67% availability and have no built-in redundant systems. What does this mean for downtime? With a Tier 1 data center, you can have up to 28.8 hours of interruption per year. This may sound insignificant for an individual or small business but having this amount of downtime spread out throughout the year can really impact medium and large businesses. This is not an ideal solution for large business or enterprise customers that rely on their website or applications to be up and running all of the time.

Tier 2 data center

A Tier 2 data center is offers a slight improvement over Tier 1 data center facility. With a Tier 2 facility, you will have 6.8 hours less of downtime per year. Tier 2 data center features 99.75% availability with 22 hours of downtime per year.

Tier 2 data centers feature redundant systems. What does this mean? It means that they have backup systems for mission-critical infrastructure within the data center. Mission-critical infrastructure includes power feeds, internet and network entrances, HVAC, cooling system redundancy, temporary backup battery storage and uninterruptible power supply (UPS) systems and backup diesel generators. All of this in an effort to prevent data center downtime and interruption.

Tier 3 data centers

This is perhaps the most common certification for a data center. What is a Tier 3 data center? Tier 3 data centers are often referred to as having three 9s. Tier 3 data centers offer a large jump in data center availability over Tier 1 and Tier 2 data centers. In fact, a Tier 3 data center has 99.982% availability with only 1.6 hours of downtime per year.

Compare those numbers against Tier II data center that has 22 hours of downtime per year. That is truly a substantial jump in terms of availability. You should always select a Tier 3 data center over a Tier 1 or Tier 2 data center even if the pricing is slighting higher.

Tier 4 data center

We are on the last data center uptime certification. Tier 4 data centers feature the highest classification for a data center facility. They are not as common as you would think and are typically reserved for large enterprise customers, hyperscale and wholesale data center providers, cloud service providers (CSPs) and government agencies.

Tier 4 data centers are rated at 99.995% availability. This is a substantial jump even over Tier 3 data centers. With a Tier 4 data center facility, you can expect less than .8 hours of downtime per year. That is just 48 minutes of downtime over 365 days. Compare that to 96 minutes of downtime with a Tier 3 facility.

In terms of data center redundancy, Tier 4 facilities have the most redundant systems for mission-critical infrastructure available. To some, it may even seem like overkill but it is a necessary evil to ensure this level of uptime. Tier 4 data centers feature 2N+1 redundancy for critical infrastructure. This means that the data center operates two times what is required for each system plus a backup.

Tier 3 vs tier 4? Which is better?

Tier 3 and Tier 4 data centers are great options for your hosting infrastructure. Is there a big cost difference between Tier 3 vs Tier 4 data center facilities? Yes and no. It really depends on the location and market where the data center is located. Tier 4 data centers may not be available in the market you need. In this case, a Tier III data center will do just fine.

The cloud is also another factor to consider as you build out your IT infrastructure. The cloud comes with built in redundancy in the form of having multiple availability zones (AZs) where cloud server and storage infrastructure is hosted. When you add the cloud with physical infrastructure, you get the best of both worlds and further reduce the chances of disruption from a data center or cloud outage perspective.

One last point to consider, just because a data center is a certified Tier 1, Tier 2, Tier 3 or Tier 4 does not mean that it has to go down for 1.6 hours each year. In fact, there are numerous Tier III data center facilities that have not experienced downtime in 2 years, 5 years, 10 years or more. An important question to ask a data center or colocation provider is a history of their most recent data center outages.


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