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.
By submitting your personal information, you agree that TechTarget and its partners may contact you regarding relevant content, products and special offers.
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