This 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 (use RMAN default value)

This parameter is no longer valid in Oracle 10g.

See also:

RMAN Backup with an External Backup Library

Oracle documentation