to view all the backup configuration settings we should type
RMAN> show all;
Basic configuration’s meaning is explained under this LINK
Channel is a connection to a db server session. RMAN uses channels to perform most tasks. With CONFIGURE CHANNEL command we can configure default behavior of all new channels.
One can ALLOCATE CHANNEL to open up one time or manually use channel and configure channel.
It is possible to use parallelism – more channels at once.
One can toggle on/off in RMAN CONFIGURE. When turned on, RMAN will not backup any element that has already been backed up, only the changed blocks.
RMAN> configure backup optimization on;