Insight 12.1
Oracle RAC (Real Application Clusters) is a 'shared-everything' architecture. This allows multiple instances to access the same physical database simultaneously. This protects against the failure of a single server (node) and enables load balancing.
Oracle Data Guard, on the other hand, is based on a primary and one or more standby databases. Data is copied from the primary to the standby site via redo log transport. Data Guard protects against site outages, data corruption, or disasters. The main difference: RAC shares storage, while Data Guard replicates data to separate storage. In a RAC cluster, all instances are active; with Data Guard, the standby site is usually in standby mode. However, Active Data Guard allows read-only access to the standby database during replication. In modern architectures, both are often combined (Maximum Availability Architecture).
In summary: RAC for local scalability, Data Guard for security in the event of a total site failure.
Oracle RAC vs Oracle Data Guard
Oracle RAC vs Oracle Data Guard: The two pillars of Oracle High Availability.
Oracle RAC (Real Application Clusters) is a 'shared-everything' architecture. This allows multiple instances to access the same physical database simultaneously. This protects against the failure of a single server (node) and enables load balancing.
Oracle Data Guard, on the other hand, is based on a primary and one or more standby databases. Data is copied from the primary to the standby site via redo log transport. Data Guard protects against site outages, data corruption, or disasters. The main difference: RAC shares storage, while Data Guard replicates data to separate storage. In a RAC cluster, all instances are active; with Data Guard, the standby site is usually in standby mode. However, Active Data Guard allows read-only access to the standby database during replication. In modern architectures, both are often combined (Maximum Availability Architecture).
In summary: RAC for local scalability, Data Guard for security in the event of a total site failure.