An N+1 topology includes some number of primary nodes and one secondary node. You do not have to configure the primary nodes and secondary node identically. The primary nodes actively provide application services. The secondary node need not be idle while waiting for a primary to fail.
The secondary node is the only node in the configuration that is physically connected to all the multihost storage.
If a failure occurs on a primary, Sun Cluster fails over the resources to the secondary, where the resources function until they are switched back (either automatically or manually) to the primary.
The secondary must always have enough excess CPU capacity to handle the load if one of the primaries fails.
The following figure illustrates an N+1 configuration.