Most every data center request for proposal or list of services will have technical terms like uptime and tier classification that can confuse a business. Here is a precise explanation of these terms so that you can make better and informed data center decisions.

All You Need to Know About Tier ClassificationThe tier classification was introduced by the Uptime Institute, which was founded in 1993. The tier certification is a global standard and is accepted widely as a benchmark for describing and comparing availability and reliability amongst data centers.

Tier I is the most basic data center infrastructure with a single path for cooling and power distribution, providing 99.671% availability. There is no built in redundancy in a Tier I data center.

Tier II introduces some redundant components, but still maintains a single path for cooling and power distribution and offers 99.741% availability.

Tier III differs by offering a concurrently maintainable infrastructure and an availability of 99.982%. Concurrent maintainability is the ability for systems in the topology to be bypassed and made offline at certain points for emergency repairs without affecting computing availability. Tier III data centers also have redundant components and have multiple active paths for cooling and power distribution.

Rated-4 data centers are at the highest end of data centers and offer a phenomenal 99.995% of availability. The main differing factor is that Rated-4 data centers are fault tolerant. Fault tolerance indicates that the data center will continue to be available in the event of any component failure and is achieved by providing the highest level of redundancy. At the extreme, this infrastructure will have two of everything so it can cater to any disaster situation.

For more details on data center infrastructure and for expert advice on build vs buy with regards to data centers, get in touch with us at for a free consultation. By the way, we deliver 99.995% uptime!

Alex Carroll

Alex Carroll

Managing Member at Lifeline Data Centers
Alex, co-owner, is responsible for all real estate, construction and mission critical facilities: hardened buildings, power systems, cooling systems, fire suppression, and environmentals. Alex also manages relationships with the telecommunications providers and has an extensive background in IT infrastructure support, database administration and software design and development. Alex architected Lifeline’s proprietary GRCA system and is hands-on every day in the data center.