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Failover is the constant capability to automatically and seamlessly switch to a highly reliable backup. This can be operated in a redundant manner or in a standby operational mode upon the failure of a primary server, application, system or other primary system component.
The main purpose of failover is to eliminate, or at least reduce, the impact on users when a system failure occurs.
This term is also known as fallover.
Failover for a server uses a heartbeat cable connecting two servers. As long as the pulse or heartbeat continues between the two servers, the secondary server will not initiate its instances. However, any change in the pulse of the primary server will trigger the secondary server to take over the work of the primary and send a message to the technician or data center, which will then be responsible for bringing the primary server back online. Alternately, some systems simply alert the technician or center personnel, who then manually initiate the change to the secondary server. This is called an automated with manual approval configuration.
By 2005, technology had developed using storage area networks (SAN), allowing connectivity among servers and data storage systems. This provided for multiple paths, each of which used all the components between the server and the system. Multiple paths and redundant components help to assure a viable path in the event of component failure causing any one path to fail, and increase the capacity for automatic failover.
Virtualization, which uses a virtual machine or pseudomachine with host software to create a simulated computer environment, has allowed failover to be less dependent upon physical hardware.