Oracle Data Guard

Data Guard Benefits

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Disaster recovery and high availability

Data Guard provides an efficient and comprehensive disaster recovery and high availability solution. Automatic failover and easy-to-manage switchover capabilities allow quick role reversals between primary and standby databases, minimizing the downtime of the primary database for planned and unplanned outages.
Complete data protection

A standby database also provides an effective safeguard against data corruptions and user errors. Storage level physical corruptions on the primary database do not propagate to the standby database. Similarly, logical corruptions or user errors that cause the primary database to be permanently damaged can be resolved. Finally, the redo data is validated at the time it is received at the standby database and further when applied to the standby database.
Efficient utilization of system resources

A physical standby database can be used for backups and read-only reporting, thereby reducing the primary database workload and saving valuable CPU and I/O cycles. A physical standby database can also be easily converted back and forth between being a physical standby database and an open read/write database, without compromising data protection. A logical standby database enables read-write access to a synchronized standby database, and/or adding local tables to the standby database that can also be updated, and/or creating additional indexes to optimize read performance.
Flexibility in data protection to balance availability against performance requirements

Oracle Data Guard offers the maximum protection, maximum availability, and maximum performance modes to help enterprises balance data availability against system performance requirements.
Protection from communication failures

If network connectivity is lost between the primary and one or more standby databases, redo data cannot be sent from the primary to those standby databases. Once connectivity is re-established, the missing redo data is automatically detected by Data Guard and the necessary archive logs are automatically transmitted to the standby databases. The standby databases are resynchronized with the primary database, with no manual intervention by the administrator.
Centralized and simple management

Data Guard Broker automates the management and monitoring tasks across the multiple databases in a Data Guard configuration. Administrators may use either Oracle Enterprise Manager or the Broker’s own specialized command-line interface (DGMGRL) to take advantage of this integrated management framework.
Integrated with Oracle database

Data Guard is available as an integrated feature of the Oracle Database (Enterprise Edition) at no extra cost.

Data Guard Protection Modes

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Maximum Availability

This protection mode provides the highest level of data protection that is possible without compromising the availability of a primary database. Transactions do not commit until all redo data needed to recover those transactions has been written to the online redo log and to at least one synchronized standby database. If the primary database cannot write its redo stream to at least one synchronized standby database, it effectively switches to maximum performance mode to preserve primary database availability and operates in that mode until it is again able to write its redo stream to a synchronized standby database.

This mode ensures that no data loss will occur if the primary database fails, but only if a second fault does not prevent a complete set of redo data from being sent from the primary database to at least one standby database.

Maximum Performance

This protection mode provides the highest level of data protection that is possible without affecting the performance of a primary database. This is accomplished by allowing transactions to commit as soon as all redo data generated by those transactions has been written to the online log. Redo data is also written to one or more standby databases, but this is done asynchronously with respect to transaction commitment, so primary database performance is unaffected by delays in writing redo data to the standby database(s).

This protection mode offers slightly less data protection than maximum availability mode and has minimal impact on primary database performance.

This is the default protection mode.

Maximum Protection

This protection mode ensures that zero data loss occurs if a primary database fails. To provide this level of protection, the redo data needed to recover a transaction must be written to both the online redo log and to at least one synchronized standby database before the transaction commits. To ensure that data loss cannot occur, the primary database will shut down, rather than continue processing transactions, if it cannot write its redo stream to at least one synchronized standby database.

Because this data protection mode prioritizes data protection over primary database availability, Oracle recommends that a minimum of two standby databases be used to protect a primary database that runs in maximum protection mode to prevent a single standby database failure from causing the primary database to shut down.

Oracle Data Guard

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Oracle Data Guard is the most effective and comprehensive data availability, data protection and disaster recovery solution for enterprise databases.

Data Guard delivers:

Reliability– optimum data protection and availability. You always know the state of your standby database and it can very quickly (in seconds), assume the primary role.
Lower cost and complexity – Data Guard's mature capabilities and rich management interface are included features of Oracle Enterprise Edition.
Maximum return on investment – All standby databases can be utilized for production purposes while in standby role. Idle resources are eliminated.