Failover is an IT strategy for making systems more fault tolerant and services more highly available. Failover also refers to a backup operational mode where the functions of a system component (such as a processor, server, network or database) are assumed by secondary system components when the primary component becomes unavailable. The failover process automatically offloads the primary component’s tasks to a standby system component, minimizing impact to the system’s end users. Failover can apply to any aspect of a system, including individual computers, networks, servers, data center components, storage devices and connection paths. Automatic failover means that normal functions can be maintained despite interruptions caused by equipment problems.
Failover and switchover are similar terms; however, failover is automatic while switchover requires human intervention. Certain systems intentionally do not failover automatically but require human intervention. Known as “automated with manual approval,” it runs automatically once a human has approved the failover. Systems designers usually provide failover capability in servers, systems or networks that require near-continuous availability and a high degree of reliability. Server failover often uses a “heartbeat” cable connecting two servers. As long as the heartbeat continues between the two servers, the secondary server will not take over the primary server’s tasks. Any change in the heartbeat of the primary server triggers the secondary server to take over and notify a data center technician that the primary server is offline.
Virtualization software can make failover less dependent on physical hardware by using a virtual machine as a secondary component. Failover occurs through the process of migration, in which a running virtual machine is moved from one physical host to another, with little or no disruption in service. System replication is the process recommended by SAP to ensure the high availability and disaster recovery of SAP HANA databases. SUSE Linux Enterprise Server for SAP Applications includes support for SAP HANA System Replication to automate the failover process.