A Data Guard configuration consists of one production database and one or more standby databases. The database in a Data Guard configuration are connected by Oracle Net and may be dispersed geographically. There are no restrictions on where the databases are located, provided they can communicate with each other.
You can manage primary and standby databases using the SQL command-line interface or the Data Guard broker interfaces, including a command-line interface DGMGRL and a graphical user interface that is integrated in Oracle Enterprise Manager.
Primay Database
A Data Guard configuration contains one production database, also referred to as the primary database, that functions in the primary role. This is the database that is accessed by most of your applications.
The primary database can be either a single-instance Oracle database or an Oracle Real Application Clusters (RAC) database.
Standby Databases
A standby database is a transactionally consistent copy of the primary database. Using a backup copy of the primary database, you can create up to 9 standby databases and incorporate them in a Data Guard configuration. Once created, Data Guard automatically maintains each standby database by transmitting redo data from the primary database and then applying the redo to the standby database.
Similar to a primary database, a standby database can be either a single-instance Oracle database or an Oracle RAC database.
The types of standby databases are as follows: