A cluster in active/passive mode processes all the data on one “active” server, which is then replicated to a “passive” server or servers. This essentially creates a functional backup ready to take over the “active” server’s tasks in case of a failure.
The active/passive cluster is also used to increase server availability. However, during the initial configuration, emphasis must be put on the “passive” server’s setup, which has to be identical to the “active” server to achieve redundancy and enable full replacement. Another popular option to increase availability is an active/active cluster mode.