Tier Ratings Explained
Updated: Apr 21
If you have been around the data center industry you have no doubt heard claims of Tier III and Tier IV rated data centers. Sometimes, companies want or need to know how their own data centers measure up. Many co-Location providers will market their data centers referring to Tier levels. You will hear people refer to Uptime tiers and TIA-942 tiers, certifications and compliance but what does this all mean? What is the difference? In this article we hope to make some sense of it all and help give a high-level overview of two popular data center rating systems.
The two most commonly cited rating systems are the Uptime Institute’s Tier Standard and the ANSI/TIA-942 Telecommunications Infrastructure Standard for Data Centers. These standards overlap in some areas but are independently maintained and administered by different organizations.
Uptime Institute’s Tier Standards
The Uptime Institute is a global for-profit company that created and administers the Tier Standards & Certifications for Data Centers. They offer three certification programs for designing, building and operating data centers. Additionally, they provide thought leadership, end user forums, research and advisory services for member companies across the globe. The UI and their Data Center Site Infrastructure Tier Standard is widely recognized across the data center industry and provide performance standard requirements for four Tier Levels summarized below and in Table 1. At a high level the four levels can be summarized as follows:
Tier I: Basic Site Infrastructure. Non-redundant capacity components and distribution pathways.
Tier II: Redundant Site Infrastructure Capacity Components: A capacity component such as an air handler, generator or UPS can be shutdown for maintenance or failure without affecting capacity.
Tier III: Concurrently Maintainable Site Infrastructure: This includes redundant capacity components like Tier II sites and redundant pathways, so all systems and pathways are concurrently maintainable.
Tier IV: Fault Tolerant Infrastructure: A fault tolerant data center has multiple, independent, physically isolated systems that provide redundant capacity components and multiple, independent, diverse, active distribution paths simultaneously serving the critical environment.
Courtesy Uptime Institute, LLC. Data Center Site Infrastructure Tier Standard.
A few things to point out regarding the UI Tier Standard:
The standard applies to the mechanical and electrical site infrastructure only.
A data center is only as good as the weakest component or system. For example, a data center with a Tier IV electrical system and a Tier III mechanical system can only achieve an overall Tier III rating.
Only UI can certify a data center.
UI provides an accreditation program for design professionals so they can better advise their clients on Tier rated design topologies, but they cannot certify data centers. Completion of the program allows professionals to call themselves an Accredited Tier Designer or ATD.
A Tier-Certified Design means that the design documents meet the Tier requirement.
A Tier-Certified Constructed facility means that the facility has been constructed to Tier-Certified design documents and demonstrates performance compliance.
Enterprising companies eager to take advantage of UI’s notoriety, but not interested in spending the time or money on certification by UI, may call their facility Tier compliant. Cloud or Colo companies that have multiple data centers may market their sites as being based on a Tier certified design without having the UI certification for the specific site. If you are ever in doubt you can ask the company to produce their certification foil, a badge that includes their certification number, obtained from UI.
ANSI/TIA-942 Telecommunications Infrastructure Standards for Data Centers
TIA-942 Telecommunications Infrastructure Standards for Data Centers is issued by a non-profit organization, is accredited by ANSI and covers all aspects of the physical data center including site location, architecture, security, safety, fire suppression, electrical, mechanical and telecommunication systems. Its three areas of focus include cabling design, facility design and network design. It was develop by the TIA TR-42.1.1 Network Distribution Nodes subcommittee by architects, engineers, consultants, end users and manufacturers.
TIA-942 is primarily a telecommunications infrastructure standard but about half of the content deals with facility requirements. Included is an Informative Annex with general architectural, structural, electrical, mechanical and telecommunications recommendations and requirements. The requirements are organized in 4 rating classifications.
Rated-1: Basic Site Infrastructure: A data center which has single capacity components and a single, non-redundant distribution path serving the computer equipment. Rated-2: Redundant Capacity Component Site Infrastructure: A data center which has redundant capacity components and a single, non-redundant distribution path serving the computer equipment.
Rated-3: Concurrently Maintainable Site Infrastructure: A data center which has redundant capacity components and multiple independent distribution paths serving the computer equipment. Typically, only one distribution path serves the computer equipment at any time. The site is concurrently maintainable which means that every capacity component, including elements which are part of the distribution path, can be removed/replaced/serviced on a planned basis without disrupting the IT capabilities to the End-User. Rated-4: Fault Tolerant Site Infrastructure: A data center which has redundant capacity components and multiple, active independent distribution paths serving the computer equipment. The data center allows concurrent maintainability and one (1) fault anywhere in the installation without causing downtime.
If the 4 rating levels for TIA-492 appear almost identical to the UI tier levels it’s because they were born out of the UI standard early on. In fact, TIA-942 levels where referred to as ‘tier’ levels until 2014 when the terms ‘rating’ or ‘rated’ where adopted to avoid confusion and probably a legal confrontation with UI.
Besides the terms ‘tier’ and ‘rating’ there are other differences under the hood between the two standards. For example, UI requires the use of prime rated generators but TIA-942 permits the use of standby rated generators. UI also requires cooling capacities to be able to handle the Extreme Annual Design Conditions based on the data center location while TIA-942 standard is not as strict.
Unlike UI, TIA-942 certification can be obtained by engaging an independent auditor who is accredited by the standard organization. The organizing body offers training and accreditation programs for consultants and auditors who will be licensed to certify designs and data centers.
UI and TIA-942 Summary
The two rating systems can be summarized as follows:
UI Tier Standard is managed and certified only by UI.
TIA-942 Standard is managed by a non-profit organization committee and certification can be completed by any accredited auditor.
UI Tier Standard evaluates the electrical and mechanical site infrastructure topology.
TIA-942 Rating includes, in addition to the electrical and mechanical site infrastructure, cabling, network, site, architectural and structural design elements.
The main take away is there are many differences between the two standards and having one does not guarantee the other. When evaluating co-lo or cloud providers be aware of the differences and terms such as ‘tier compliant’ or ‘compliant design’. And for your own facilities, think carefully if you need to meet one or both standards and consider using an accredited data center consultant to help you navigate.