With the hot standby database, you actually use only one database at a time. The second database is constantly in recovery mode. As an archived redo log file is generated, it is copied over to the remote site and applied to the database. In the event of a failure of the primary database, you complete the recovery process and bring up the standby database.

With this facility, you will have to maintain redundant computer and storage systems, and in the case of a recovery, you will have lost any committed transactions that have not been moved to an archived log file. However, you will not need to maintain a high-speed communication line between the databases as you must with replication. In fact, the connection does not even have to be continuous.