RMAN backup copy - read once and write many?
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.