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99.999 (Five Nines or Five 9s)

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99.999 (Five nines or Five 9s) - definition(s)

99.999 (Five nines or Five 9s) - In computers, 99.999 (often called "five 9s") refers to a desired percentage of availability of a given computer system. Such a system would probably have what some refer to as high availability. As Evan Marcus, Principal Engineer at Veritas Software, observes, 99.999 availability works out to 5.39 minutes of total downtime - planned or unplanned - in a given year.

In one view, there are three approaches to 99.999 (or even 100) percent availability:

   * Special systems that are designed for high availability, such as those from Tandem (Compaq) and Stratus, in which components are duplicated so that a backup component is always available. These tend to be expensive, requiring redundancy of components in which the redundant component is seldom used.
   * Shared component systems that are built so that one active system can back up another active system if one of them fails.
   * Clustering, a variation of the second approach, in which matched components do not necessarily have to be duplicates of each other

Related glossary terms: Chief Information Officer (CIO), business integration, business process, systems thinking, clean room technique (clean room design), work breakdown structure, B2E (Business2Employee or Business-to-Employee), Total Quality Management (TQM)

[Category=Data Management ]

Source:, 03 July 2013 09:57:17, External

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