Wy I see more than one backup images in "Rolling Forward Image Copies" Backup Strategy

Oracle 19.18

For our strategy for cyber recovery vault we are using incrementally updated image copies. 

The product is rubrik and these kind of backup is made to different NFS Shares.

To protect the production against too high a load, we make the backup on the standby side of dataguard.

run

{

sql 'alter system set "_backup_file_bufcnt"=16 scope=memory';

sql 'alter system set "_backup_file_bufsz"=4194304 scope=memory';

sql 'alter system set "_backup_disk_bufcnt"=16 scope=memory';

sql 'alter system set "_backup_disk_bufsz"=4194304 scope=memory';

# ORA-27054: NFS file system where the file is created or resides is not mounted