RMAN Mirroring Backups

It is possible to multiplex up to 4 copies per set at runtime:

run {
    set backup copies 2;
    backup full
           format '/orabackup1/rman/TARGDB/backup_db_%d_S_%s_P_%p_T_%t'
                , '/orabackup2/rman/TARGDB/backup_db_%d_S_%s_P_%p_T_%t'
           (database);
}