This parameter defines the maximum size in KB of save sets created by RMAN with an external backup library, that is, backup_dev_type = rman_util|rman_disk|rman_stage.
Syntax
rman_maxsetsize = <number>
Default value: 0 (no limit)
Note
This parameter was previously called rman_setsize.
See also:
RMAN Backup with an External Backup Library
Oracle documentation