The figure shows two nodes, one active and one passive. Each node has local storage. An Oracle home for the middle tier is installed in the local storage each node. There is also a shared storage, which is needed only if you plan to use OracleAS JMS with file-based message persistence.

Each node is also associated with an alias:

During runtime, the active node is associated with a virtual hostname and IP address. The active node also has access to the shared storage.

If node 1 (the active node) fails, node 2 takes over. The virtual hostname and IP address becomes associated with node 2, and node 2 gets access to the shared storage.