tape_size 

Storage size in gigabytes (G), megabytes (M) or kilobytes (K) for the tapes that are used for database backups and for backing up redo log files.

Syntax: tape_size = <size>K|<size>M|<size>G

Default:  1200M

The physical tape size (tape length * write density) is configured by this parameter. If you use software or hardware compression for files, this parameter specifies the total size of the files that will fit on the tape after compression. The largest file for backup should not be larger than the value specified in tape_size (after compression, when applicable).

See Parameter tape_size.