TIERS of Data Center
Tier I Data Center Infrastructure
Basic Data Center
A Tier I data center is susceptible to disruption from both planned and unplanned activity. It has computer power distribution and cooling, but it may or may not have a raised floor, a UPS, or an engine generator. The critical load on these systems is up to 100% of N. If it does have UPS or generators, they are single-module systems and have many single points-of-failure. The infrastructure should be completely shut down on an annual basis to perform preventive maintenance and repair work. Urgent situations may require more frequent shutdowns. Operation errors or spontaneous failures of site infrastructure components will cause a data center disruption.
Tier II Data Center Infrastructure
Tier II facilities with redundant components are slightly less susceptible to disruptions from both planned and unplanned activity than a basic data center. They have a raised floor, UPS, and engine generators, but their capacity design is N+1, which has a single-wired distribution path throughout. Critical load is up to 100% of N. Maintenance of the critical power path and other parts of the site infrastructure will require a processing shutdown.
Tier III Data Center Infrastructure
Tier III level capability allows for any planned site infrastructure activity without disrupting the computer hardware operation. Planned activities include preventive and programmable maintenance, repair and replacement of components, addition or removal of capacity components, testing of components and systems, and more. For large sites using chilled water, this means two independent sets of pipes. Sufficient capacity and distribution must be available to simultaneously carry the load on one path while performing maintenance or testing on the other path. Unplanned activities such as errors in operation or spontaneous failures of facility infrastructure components will still cause a data center disruption. The critical load on a system does not exceed 90% of N. Many Tier III sites are designed with planned upgrades to Tier IV when the client's business case justifies the cost of additional protection. The acid test for a concurrently maintainable data center is the ability to accommodate any planned work activity without disruption to computer room processing.
Tier IV Data Center Infrastructure
Tier IV provides site infrastructure capacity and capability to permit any planned activity without disruption to the critical load. Fault-tolerant functionality also provides the ability of the site infrastructure to sustain at least one worst-case, unplanned failure or event with no critical load impact. This requires simultaneously active distribution paths, typically in S+S configuration. Electrically, this means two separate UPS systems in which each system has N+1 redundancy. The combined critical load on a system does not exceed 90% of N. Because of fire and electrical safety codes, there will still be downtime exposure due to fire alarms or persons initiating an Emergency Power Off (EPO). Tier IV requires all computer hardware have dual power inputs as defined by The Institute's Fault Tolerant Power Compliance Specifications Version 2.0, which can be found at www.uptimeinstitute.org. The acid test for a fault tolerant data center is the ability to sustain an unplanned failure or operations error without disrupting computer room processing. In consideration of this acid test, compartmentalization requirements must be addressed.