Oracle RAC on Extended Distance Clusters

A special implementation of Oracle RAC lets you add an extended distance cluster, also called a stretched cluster, metro cluster, campus cluster, or geo cluster. With an extended distance cluster, components are deployed across two or more data center locations, allowing them to continue to function if one location fails. In normal operation, all nodes at all locations will be active. The distance for an extended Oracle RAC is determined by the type failure against which the Oracle RAC should be protected.

To make the Oracle RAC survive a fire in the server room, for example, it would be sufficient to have half of the nodes and the shared storage mirror in another server room, in another fire protection sector. To protect the Oracle RAC against an airplane crash or a terrorist attack, the distance between the Oracle RAC parts should be increased to at least a couple of miles. When making the decision regarding how far to stretch the cluster, remember that every mile adds latency for the network and the I/O operations, which can result in slow performance on a daily basis; this might not be a worthy tradeoff against the rare chance of losing the entire data center.