exec_parallel

This parameter specifies the maximum number of parallel copy processes.

Syntax: exec_parallel = <number>

Default value: 0 
The number of parallel copy processes corresponds to the number of backup devices available (tape devices/disks) in this case. If you use option
-k only  to determine the compression rates, -w only_dbv to verify the database, or –d rman_prep to prepare for RMAN backups, the number of parallel copy processes corresponds to the number of disks (or logical volumes) on which the database files reside.

·        Backup on tape

The value n should be less than or equal to the number of backup devices. If you define a value n less than the number of tape devices, this means that you can only use n of the available tape devices in parallel. If a tape change should then become necessary in one of the tape devices used in parallel, there is an automatic change to the next free backup device and the backup continues there.

·        Backup to disk

The number of parallel copy processes can be greater than the number of disks defined in backup_root_dir or stage_root_dir (but not greater than 255). One or more disks are then written by several processes at the same time. If you choose the number of copy processes n to be less than the number of disks, this means that you can only use n of the available disks in parallel. If one of the disks used in parallel is full, there is an automatic change to the next disk which has not been used and backup continues  there.

·        Restoring

The maximum number of parallel copy processes which BRRESTORE can restore is the number of parallel copy processes used in the backup. The number of copy processes can be reduced.