Failover

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In computing, failover is the capability to switch over automatically to a redundant or standby computer server, system, or network upon the failure or abnormal termination of the previously active application,^[1] server, system, or network. Failover happens without human intervention and generally without warning, unlike switchover.

Systems designers usually provide failover capability in servers, systems or networks requiring continuous availability and a high degree of reliability.

At server-level, failover automation takes place using a "heartbeat" cable that connects two servers. As long as a regular "pulse" or "heartbeat" continues the main server to the second server, the second server will not initiate its systems. There may also be a third "spare parts" server that has running spare components for "hot" switching to prevent down time.

The second server will immediately take over the work of the first as soon as it detects an alteration in the "heartbeat" of the first machine. Some systems have the ability to page or send a message to a pre-assigned technician or center.

Some systems, intentionally, do not failover entirely automatically, but require human intervention. This "automated with manual approval" configuration runs automatically once a human has approved the failover.

Failback, conversely, involves the process of restoring a system/component/service in a state of failover back to its original state (before failure).

The use of virtualization software has allowed failover practices to become less reliant on physical hardware.

[edit] See also

• Safety engineering
• Data reliability
• Fault-tolerance
• High-availability cluster
• Log shipping

[edit] References

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