About RMAN channels

•An RMAN channel corresponds to one server session and it represents one stream of data to a device type.

•When you run a command that requires to use any server session then RMAN automatically allocates channel with the option specified in CONFIGURE command, if you don't explicitly allocate any channel.

•In the settings for which RMAN automatically allocate channel are.

CONFIGURE DEVICE TYPE ... PARALLELISM
CONFIGURE DEFAULT DEVICE TYPE
CONFIGURE CHANNEL

•You can override automatically allocated channel by explicitly specifying ALLOCATE CHANNEL within run block as follows,

RUN
{
ALLOCATE CHANNEL c1 DEVICE TYPE sbt;
BACKUP DATABASE;
}

•If you have any three above types of CONFIGURE settings then RMAN automatically allocates channel when you perform BACKUP, RESTORE, DELETE command or command within RUN block.

•The number of channels allocation is done by CONFIGURE DEVICE TYPE ... PARALLELISM is based on parallelism settings. If setttings is
CONFIGURE DEVICE TYPE DISK PARALLELISM 3;
then RMAN allocate 3 channels.

•Channel name is defined by ORA_devicetype_n, where

devicetype refers to the user's device type (such as DISK or sbt_tape) and
n refers to the channel number.

The thing need to know that RMAN output always displays sbt_tape whether the input is sbt or sbt_tape. If I have CONFIGURE DEVICE TYPE sbt PARALLELISM 2; then channel 1 will be named as ORA_SBT_TAPE_1 and channel 2 will be named as ORA_SBT_TAPE_2.

•Channel name prefix by ORA_ are reserved for RMAN. You cannot manually allocate a channel with a name that begins with ORA_.