The figure shows two nodes, one active and one passive. Each node has local storage. There is also a shared storage where the Oracle home for the middle tier is installed.

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.