RMAN backup copy - read once and write many? I am trying to find out what happens in this scenario: 

BACKUP COPIES 2 


What actually happens in the BACKUP COPIES above?  Does Oracle RMAN read the data files each time for each separate copy?  Or does it read only once and write as many copies as specified?
In case you specify COPIES 2 each block is read once and written two times to backupset copies. The two backupset copies are supposed to be bit-to-bit identical. Both copies have the same backupset key (BS_key) in RMAN. You cannot mix tape and disk copies - either both copies go to DEVICE DISK or both to DEVICE SBT.