RAC and Data Guard

Real Application Clusters

RAC runs one database across several servers that share storage. If one node fails, the others keep serving. Applications connect to a service, not to a single server.

Data Guard

Data Guard keeps a synchronized standby database on separate hardware. The standby applies redo from the primary and can take over for disaster recovery.

Switchover and Failover

ALTER DATABASE SWITCHOVER TO STANDBY;

Switchover is a planned role swap with no data loss. Failover activates the standby after a primary outage and, with the fastest settings, may accept a small amount of loss.

Key Points

• RAC adds node-level resilience.
• Data Guard provides a disaster-recovery standby.
• Switchover is planned; failover is automatic.
• Combine RAC and Data Guard for maximum availability.