Oracle Data Guard can be deployed to maintain standby databases at a secondary site. These standby databases are maintained as synchronized copies of the production database.
If the production database becomes unavailable because of a planned or an unplanned outage, Data Guard can switch the standby database to the production role, thus minimizing the downtime associated with the outage, and preventing any data loss.
The ability to create standby databases was first offered as a feature in Oracle 8i, although users were creating manual standby databases since Oracle 7.3.
Features introduced in Oracle 8i:
- Read-only physical standby database
- Managed recovery of standby
- Remote archiving of redo log files
Features introduced in Oracle 9i:
- Integrated zero-data-loss capability
- Data Guard Broker w/ Data Guard Manager GUI
- Command Line Interface (CLI)
- Switchover and Failover operations
- Automatic gap resolution
- Automatic Synchronization
- Logical standby databases
- Maximum protection / availability
- Enhanced Data Guard Broker
- Cascaded redo log destinations
Features introduced in Oracle 10g:
- Real-time apply
- Recovery through OPEN RESETLOGS
- Simplified configuration with VALID_FOR attribute
- Standby redo log support on logical standby databases
- Improved redo transmission security
- Improved support for RAC
- Zero downtime instantiation of logical standby databases
- Fast-start Failover
- Flashback Database across Data Guard switchovers
- Asynchronous Redo Transmission
- Faster Redo Apply failover
Features introduced with Oracle 11g:
- Standby databases can remain open while doing recovery
- Heterogeneous platform support (standby can be on a different platform). For example, production on Linux and standby on Windows.
Data guard technology ships with the Oracle database server. Enterprise edition licenses are required for ALL of the primary and standby database servers.
 Advantages offered
- Data Guard provide high availability for database servers
- Reduces the amount of human intervention required to switch between sites
- There is no distance limitation - the secondary site can be located thousands of kilometres away.
Oracle provides both GUI and command-line tools for managing Data Guard configurations.
With appropriately set up, DBAs can facilitate failovers or switchovers to alternative hosts in alternative locations.