1.4.2 Failover support and disaster recovery

Faults are distinguished from failures by the fact that the faults of the system may or may not cause failures. If faults exist in a system and, in a given scenario, no action is performed with the faulty component that may expose the fault, then the failure will not happen.

Failures are distinguished from disasters by the fact that failures may or may not cause disasters. While failures tend to be specific and localized, the disasters tend to be widespread in their scope, usually sudden and highly disruptive. Disasters can be natural, man-made, or a combination of the two. Disasters can be earthquakes, volcanic eruptions, fire, power failure, theft, terrorist attack, and so on.

In failover solutions the tasks of failed components are assumed by the operational components. Disaster recovery solutions are implemented to localize the scope of the failures and to minimize or eliminate any disruptions that the disaster might otherwise have caused.
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