Find RMAN Backup Statistics

You can query the view V$BACKUP_SYNC_IO (for synchronous tape devices) to obtain the average MB transfer speed from RMAN to the tape device (or intermediary software if using the obk interface):

SQL> select avg(EFFECTIVE_BYTES_PER_SECOND)/1024/1024 MB_per_s
       from V$BACKUP_SYNC_IO
      where DEVICE_TYPE='SBT_TAPE';
MB_PER_S
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16.1589822