Channel is a link that RMAN requires to link to target database. This link

is required when backup and recovery operations are performed and recorded.

This channel can be allocated manually or can be preconfigured by using

automatic channel allocation.

The number of allocated channels determines the maximum degree of

parallelism that is used during backup, restore or recovery. For example, if

you allocate 4 channels for a backup operation, 4 background processes for the

operation can run concurrently.

Parallelization of backup sets allocates multiple channels and assigns

files to specific channels. You can configure parallel backups by setting a

PARALLELISM option of the CONFIGURE command to a value greater than 1 or by

manually allocating multiple channels.

RMAN> CONFIGURE DEVICE TYPE PARALLELISM 2 BACKUP TYPE TO COMPRESSED

BACKUPSET;