Oracle Data Guard ensures high availability, data protection, and disaster recovery for enterprise data. Data Guard provides a comprehensive set of services that create, maintain, manage, and monitor one or more standby databases to enable production Oracle databases to survive disasters and data corruptions. Data Guard maintains these standby databases as copies of the production database. Then, if the production database becomes unavailable because of a planned or an unplanned outage, Data Guard can switch any standby database to the production role, minimizing the downtime associated with the outage. Data Guard can be used with traditional backup, restoration, and cluster techniques to provide a high level of data protection and data availability.
With Data Guard, administrators can optionally improve production database performance by offloading resource-intensive backup and reporting operations to standby systems.
A Data Guard configuration consists of one production (or primary) database and up to nine standby databases. The databases 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 that they can communicate with each other. However, for disaster recovery, it is recommended that the standby databases are hosted at sites that are geographically separated from the primary site.
In a Data Guard configuration, the switchover and failover concepts are also very important. By performing a switchover, it’s possible to change the roles of the primary and standby databases and change the direction of the redo shipping. Failover is the option that we must use to open a standby database to user connection in read/write mode, when the primary database is inaccessible.
There are user interfaces to monitor and administrate a Data Guard configuration. These are SQL*Plus, Oracle Enterprise Manager Cloud Control, and Data Guard broker command-line interface (DGMGRL).