Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

Network managers must prepare for fires, earthquakes, storms, and theft. Disasters can disrupt user access to data and/or data communications. A downed server or failed communication link may be disastrous if those resources are needed for critical operations. A system may provide life-support or life-saving information, or may provide mission-critical business transaction services.

A disaster plan must define a recovery procedure that brings resources back online as fast as possible, or ensures that they are operational 24/7 (24 hours a day, 7 days a week). A downed business transaction server could mount up losses in the millions of dollars over only a few hours or days.

Disaster planning not only involves a plan to recover from the disaster, but also requires redundant components, systems, and even duplicate data centers that can continue operations. Systems must provide automatic failover if they are to provide high levels of service. The levels of service are gauged by metrics used throughout the industry. So-called "high-availability" systems have ratings in the "five-nines" (99.999%) availability. See "Fault Tolerance and High Availability."