Uptime Institute Data Center Tiers Explained


Your datacenter service provider claims their facility is Tier III. But, are they actually Uptime certified? What exactly is the difference is between Tier II and Tier III? Does certification matter?

With the upcoming 20 year anniversary of the Uptime Institute’s Tier Classification System, we wanted to share some information concerning the system that is now considered the global standard for third-party validation of data center critical infrastructure. 

This post was created based on a recent article in Data Center Knowledge written by Matt Stansberry, Director of Content and Publications at Uptime Institute.

 What are the Tiers?

Uptime Institute created the standard Tier Classification System to consistently evaluate various data center facilities in terms of potential site infrastructure performance, or uptime. 

The Tiers (I-IV) are progressive; each Tier incorporates the requirements of all the lower Tiers.

Tier I: Basic Capacity – A Tier I data center provides dedicated site infrastructure to support information technology beyond an office setting. Tier I infrastructure includes a dedicated space for IT systems; an uninterruptible power supply (UPS) to filter power spikes, sags, and momentary outages; dedicated cooling equipment that won’t get shut down at the end of normal office hours; and an engine generator to protect IT functions from extended power outages.

Tier II: Redundant Capacity Components – Tier II facilities include redundant critical power and cooling components to provide select maintenance opportunities and an increased margin of safety against IT process disruptions that would result from site infrastructure equipment failures. The redundant components include power and cooling equipment such as UPS modules, chillers or pumps, and engine generators.

Tier III: Concurrently Maintainable – A Tier III data center requires no shutdowns for equipment replacement and maintenance. A redundant delivery path for power and cooling is added to the redundant critical components of Tier II so that each and every component needed to support the IT processing environment can be shut down and maintained without impact on the IT operation.

Tier IV: Fault Tolerance – Tier IV site infrastructure builds on Tier III, adding the concept of Fault Tolerance to the site infrastructure topology. Fault Tolerance means that when individual equipment failures or distribution path interruptions occur, the effects of the events are stopped short of the IT operations.

Data center infrastructure costs and operational complexities increase with each Tier Level, and it is up to the data center owner to determine the Tier Level that fits his or her business’s need. A Tier IV solution is not “better” than a Tier II solution. The data center infrastructure needs to match the business application, otherwise companies can over invest or take on too much risk.

Uptime Institute recognizes that many data center designs are custom endeavors, with complex design elements and multiple technology choices. As such, the Tier Classification System does not prescribe specific technology or design criteria beyond those stated above. It is up to the data center owner to meet those criteria in a method that fits his or her infrastructure goals.

 Tier Requirements Summary:

  Tier I Tier II Tier III Tier IV
 Active capacity components 
 to support the IT load
 N  N+1  N+1  N after any failure
 Distribution paths  1  1  1 active &
 1 alternative
 2 simultaneously
 Concurrently maintainable  no  no  yes  yes
 Fault tolerance  no  no  no  yes
 Compartmentalization  no  no  no  yes
 Continuous cooling  no  no  no  yes


Tier Certification

The Tier Certification process typically starts with a company deploying new data center capacity. The data center owner decides to achieve a specific Tier level to match a business demand. Data center owners turn to Uptime Institute for an unbiased, vendor neutral benchmarking system, to ensure that data center designers, contractors and service providers are delivering against their requirements and expectations.

The first step in a Tier Certification process is a Tier Certification of Design Documents (TCDD). Uptime Institute Consultants review 100% of the design documents, ensuring each subsystem among electrical, mechanical, monitoring, and automation meet the fundamental concepts and there are no weak links in the chain. Uptime Institute has conducted over 400 TCDDs, reviewing the most sophisticated data center designs from around the world. One of the important lessons learned along the way is that some companies would achieve a TCDD, and walk away from following through on Facility Certification for any number of reasons. Some organizations were willfully misrepresenting the Tier Certification, using a design foil to market a site that was not physically tested to that standard.

The TCDD was never supposed to be a final stage in a certification process, but rather a checkpoint for companies to demonstrate that the first portion of the capital project met requirements. Uptime Institute found that stranded Design Certifications were detrimental to the integrity of the Tier Certification program. In response, Uptime Institute has implemented an expiration date on TCDDs. All Tier Certification of Design Documents awards issued after 1 January 2014 will expire two years after the award date.

Data center owners use the Tier Certification process to hold the project teams accountable, and to ensure that the site performs as it was designed. Which brings us to the next phase in a Tier Certification process: Tier Certification of Constructed Facility (TCCF).

During a TCCF, a team of Uptime Institute consultants conducts a site visit, identifying discrepancies between the design drawings and installed equipment. Their consultants observe tests and demonstrations to prove Tier compliance. Fundamentally, this is the value of the Tier Certification, finding these blind spots and weak points in the chain. When the data center owner addresses the deficiencies, Uptime Institute awards the TCCF letter, foil and plaque. Does the industry find value in this process? The clearest proof is the list of companies investing in Tier Certification. There are more Certifications underway at this moment than at any other point in the 20 year history of the Tiers.

As the IT industry moves further into the cloud and IaaS mode of service delivery, the end user has less control over the data center infrastructure than ever before. Tiers and Operational Sustainability provide third-party assurance that the underlying data center infrastructure is designed and operated to the customer’s performance requirements.

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