rman_diskratioThis parameter defines the number of disk drives used for reading datafiles by RMAN with an external backup library, that is, backup_dev_type = rman_util|rman_disk|rman_stage
.
Syntax
rman_diskratio = <number>Default: 0
(uses RMAN default value)
See also:
RMAN Backup with an External Backup Library
Oracle documentation