1.If all the nodes in the cluster are needed in order to perform adequately, then it is not HA ( High Availability) 2.RAC only makes up one piece of the MAA(Maximum Availability Architecture); it does not account for all possible problems.
RMAN channel: An RMAN channel represents one stream of data to a device type, and corresponds to one server session.
Most backup and recovery commands in RMAN are executed by server sessions. Each channel establishes a connection from the RMAN client to a target or auxiliary database instance by starting a server session on the instance. The server session performs the backup, restore, and recovery.
This example restores and recovers the tablespace, using configured channels and
letting RMAN choose the backups to use in restoring the tablespace and any needed
incremental backups and logs from disk or tape.
1. Connect to the target database and the recovery catalog database (if applicable),
and make sure the database is mounted or open. For example:
2. Take the tablespaces affected offline using ALTER TABLESPACE ... OFFLINE