Glossary

Failover

Failover indicates an operational mode in which the functions of a system-critical component (such as a processor, a network element, or a database) are assumed by secondary system components when the primary equipment becomes unavailable through either failure or scheduled down time. The capacity for automatic failover indicates that normal functions can be maintained despite the inevitable interruptions caused by problems with equipment.

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Fault tolerance

Fault-tolerant describes a computer system or component designed so that, in the event that a component fails, a backup component or procedure can immediately take its place with no loss of service. Fault tolerance can be provided with software, or embedded in hardware, or provided by some combination of both. At a hardware level, fault tolerance is typically achieved by duplexing each hardware component. Disks are mirrored. Multiple processors are "lock-stepped" together and their outputs are compared for correctness. When an anomaly occurs, the faulty component is identified and taken out of service, but the machine continues to function as usual