Some situations require a Manual Failover. For example, if an entire data center suffers a power outage (one Unity server and one Teradata system are offline) Automatic Failover is not triggered since one of the Automatic Failover conditions cannot be met. The operator must make sure that the active Sequencer is actually down before initiating a Failover (check for a power outage and not a temporary network disconnection between data centers.)
In a Manual Failover mode, the Active Sequencer process automatically resets itself as the Active Sequencer when a transient failure event, such as a temporary network issue, occurs and the user has not issued a takeover and performed work on the new Active Sequencer.