Data Center Tier Performance Standards


National Conference on Building Commissioning: May 2-4, 2007
Edward P Rafter, P.E. CxAP
Tier IV Consulting Group


The data center industry has experienced several evolutions over the past 20 years. One of the principal changes has been the development of the Tier Performance Standards. The standards provide quantifiable plateaus or Tier Levels. Tier Levels provide an objective basis for comparing the capabilities of a particular design topology against other designs as well as the associated site availability metrics for the various levels. The requirements of each Tier Level are clearly defined and provide a road map used in the design and management of the data center.

The Tier Level was developed in the early 1990s and is the foundation used by a number of data center owners/users, consultants and design professionals in establishing a “design-versus-performance” ranking approach to today’s data center projects.

Tier Level Standards and Performance Expectations

The Tier I data center has non-redundant capacity components and single non-redundant path distribution paths serving the site’s computer equipment. The data center has computer room cooling and power distribution but it may or may not have a UPS or and engine generator. The data center must be shutdown for annual predictive maintenance and repair work. Corrective maintenance may require additional shutdowns. Operation errors or spontaneous failures of infrastructure components will cause a data center disruption. As example, a Tier I data center may be suitable for small businesses where IT is intended for internal business processes

The Tier II data center has redundant capacity components and single non-redundant distribution paths serving the site’s computer equipment. They have UPS and engine generators but their capacity design is Need plus One (N+1), with a single power path. Maintenance of the critical power path and other parts of the site infrastructure will require a shutdown of computer processes. As example, a Tier II data center may be appropriate for internet-based companies without serious financial penalties for quality of service commitments.

The Tier III data center is concurrently maintainable and has redundant capacity components and multiple distribution paths serving the site’s computer equipment. Generally, only one distribution path serves the computer equipment at any time. This topology allows for any planned site infrastructure activity without disruption the computer systems operation in any way. An example of a Tier III application would include companies that span multiple time zones or whose information technology resources support automated business process.

The Tier IV data center is fault tolerant and has redundant capacity systems and multiple distribution paths simultaneously serving the site’s computer equipment. All IT equipment is dual powered and installed properly to be compatible with the topology of the site’s architecture. Fault-tolerant functionality also provides the ability of the site infrastructure to sustain at lease one worst-case unplanned failure or event with impact to the critical load. This typically includes a System+System topology. Examples of a Tier IV requirement include companies who have extremely high-availability requirements for ongoing business such as E-commerce, market transactions, or financial settlement processes.

The following is a summary of representative site availability expectations for each of the tier levels described above. The availability percentages can be considered characteristic of the operating experiences of a representative number of sites within each tier classification.

• Tier I = 28.8 hours and 99.67%
• Tier II = 22.0 hours and 99.75%
• Tier III = 1.6 hours and 99.98%
• Tier IV = 0.4 hours and 99.99%

Read the complete article here - found at the California Commissioning Collaborative Resource Library.

The Uptime Institute's tiered classification system

A four tier system that provides a simple and effective means for identifying different data center site infrastructure design topologies. The Uptime Institute's tiered classification system is an industry standard approach to site infrastructure functionality addresses common benchmarking standard needs. The four tiers, as classified by The Uptime Institute include the following:

  • Tier 1: composed of a single path for power and cooling distribution, without redundant components, providing 99.671% availability.
  • Tier II: composed of a single path for power and cooling distribution, with redundant components, providing 99.741% availability
  • Tier III: composed of multiple active power and cooling distribution paths, but only one path active, has redundant components, and is concurrently maintainable, providing 99.982% availability
  • Tier IV: composed of multiple active power and cooling distribution paths, has redundant components, and is fault tolerant, providing 99.995% availability.

Read more info here.
Be sure to check out The Uptime Institute.