Is there any way to speed up the execution time of the full RMAN backup?

With device tape I can use the rman parameter "configure backup optimization on;" ?
It would appear not: http://pages.di.unipi.it/ghelli/dida...mconc1008.html

To check the RMAN backup bottleneck, should I run 'backup validate' or are there other faster checks?
If the time for the BACKUP VALIDATE to tape is about the same as the time for a real backup to tape, then reading from disk is the likely bottleneck.
If the time for the BACKUP VALIDATE to tape is significantly less than the time for a real backup to tape, then writing to the output device is the likely bottleneck.

My configuration

Current time spent: 50 hours.
Datafiles on ASM.
Device type: sbt_tape.
CPU number:16
Oracle instance size: 4.4 TB

Multiplexing
Default maxopnefiles: 8
Default fileperset: 64

BLKSIZE= 4 MB (For SBT backups, the output buffer size can be increased using the BLKSIZE channel parameter. The default tape buffer is 256 KB).

BACKUP_TAPE_IO_SLAVES=true
LARGE_POOL_SIZE = number_of_channels * (16MB+(4 * size _of_tape_buffer)) --> 4 * (16 MB + (4 * 4MB)) = 128 MB


RMAN parameters
CONFIGURE RETENTION POLICY TO RECOVERY WINDOW OF 30 DAYS;
CONFIGURE BACKUP OPTIMIZATION OFF; # default
CONFIGURE DEFAULT DEVICE TYPE TO 'SBT_TAPE';
CONFIGURE CONTROLFILE AUTOBACKUP FORMAT FOR DEVICE TYPE SBT_TAPE TO '%F'; # default
CONFIGURE DEVICE TYPE 'SBT_TAPE' PARALLELISM 4 BACKUP TYPE TO BACKUPSET;
CONFIGURE DEVICE TYPE DISK PARALLELISM 1 BACKUP TYPE TO BACKUPSET; # default
CONFIGURE DATAFILE BACKUP COPIES FOR DEVICE TYPE SBT_TAPE TO 1; # default
CONFIGURE DATAFILE BACKUP COPIES FOR DEVICE TYPE DISK TO 1; # default
CONFIGURE ARCHIVELOG BACKUP COPIES FOR DEVICE TYPE SBT_TAPE TO 1; # default
CONFIGURE ARCHIVELOG BACKUP COPIES FOR DEVICE TYPE DISK TO 1; # default
CONFIGURE CHANNEL DEVICE TYPE 'SBT_TAPE' PARMS 'SBT_LIBRARY=/u01/app/oracle/product/19.0.0/dbhome_1/lib/libosbws.so,SBT_PARMS=(OSB_WS_PFILE=/u01/app/oracle/product/19.0.0/dbhome_1/dbs/osbwsDBNAME.ora)';
CONFIGURE COMPRESSION ALGORITHM 'MEDIUM' AS OF RELEASE 'DEFAULT' OPTIMIZE FOR LOAD TRUE;

RMAN script
run {
allocate channel dev1 device type SBT parms 'BLKSIZE=4194304,SBT_LIBRARY=/u01/app/oracle/product/19.0.0/dbhome_1/lib/libosbws.so ENV=(OSB_WS_PFILE=/u01/app/oracle/product/19.0.0/dbhome_1/dbs/osbwsDBNAME.ora)' MAXPIECESIZE 10G;
allocate channel dev2 device type SBT parms 'BLKSIZE=4194304,SBT_LIBRARY=/u01/app/oracle/product/19.0.0/dbhome_1/lib/libosbws.so ENV=(OSB_WS_PFILE=/u01/app/oracle/product/19.0.0/dbhome_1/dbs/osbwsDBNAME.ora)' MAXPIECESIZE 10G;
allocate channel dev3 device type SBT parms 'BLKSIZE=4194304,SBT_LIBRARY=/u01/app/oracle/product/19.0.0/dbhome_1/lib/libosbws.so ENV=(OSB_WS_PFILE=/u01/app/oracle/product/19.0.0/dbhome_1/dbs/osbwsDBNAME.ora)' MAXPIECESIZE 10G;
allocate channel dev4 device type SBT parms 'BLKSIZE=4194304,SBT_LIBRARY=/u01/app/oracle/product/19.0.0/dbhome_1/lib/libosbws.so ENV=(OSB_WS_PFILE=/u01/app/oracle/product/19.0.0/dbhome_1/dbs/osbwsDBNAME.ora)' MAXPIECESIZE 10G;
backup as compressed backupset incremental level 0 database include current controlfile format = 'dbname_backup_lv0_%Y%M%D_%t_%U' plus archivelog;
crosscheck backupset;
delete expired backupset;
delete noprompt obsolete;
show retention policy;
release channel dev1;
release channel dev2;
release channel dev3;
release channel dev4;
}

Best regards