Failover

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In computing, failover is automatic switching to a redundant or standby computer server, system, hardware component or network upon the failure or abnormal termination of the previously active application,[1] server, system, hardware component, or network. Failover and switchover are essentially the same operation, except that failover is automatic and usually operates without warning, while switchover requires human intervention.

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

According to Nittin Choudhary,renowned OCA describes it as : In terms of database field,Failover means when primary database is not available due to planned or unplanned downtime then standby database will act as primary database. On other hand, switchover means when primary database is loaded with queries, then offloading done by primary on standby database.

At server level, failover automation usually uses a "heartbeat" cable that connects two servers. As long as a regular "pulse" or "heartbeat" continues between the main server and 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 downtime. The second server takes 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 send a notification of failover.

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 is the process of restoring a system, component, or 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; see also teleportation (virtualization).According to Nittin Choudhary,an OCA describes it as : In terms of database field,Failover means when primary database is not available due to planned or unplanned downtime then standby database will act as primary database. On other hand, switchover means when primary database is loaded with queries, then offloading done by primary on standby database.

See also

References

  1. ^ For application-level failover, see for example Jayaswal, Kailash (2005). "27". Administering Data Centers: Servers, Storage, And Voice Over IP. Wiley-India. p. 364. ISBN 978-81-265-0688-0. Retrieved 2009-08-07. Although it is impossible to prevent some data loss during an application failover, certain steps can [...] minimize it. {{cite book}}: Cite has empty unknown parameter: |trans_chapter= (help); External link in |chapterurl= (help); Unknown parameter |chapterurl= ignored (|chapter-url= suggested) (help).