standby engine

In a two-engine DR/HA configuration, the engine that provides DR and high availability (HA) support for the active engine. In a three-engine DR/HA configuration, there can be two standby engines: one that provides high availability (HA) support for the active engine and one that provides support for the first standby engine (the engine supporting the active engine). A standby engine only replays transaction logs and does not accept network data. If the active engine fails, the standby engine becomes the active engine.