You suspect ur Rman Backup Piece Integrity !!

Problem

You need to perform a restore and recovery, but first you want to validate only that the backup pieces are available and structurally sound before you actually restore any datafiles.

Solution

You can use either the restore ... validate or validate command to verify the availability and integrity of backup pieces required by RMAN to perform the restore operation. These commands do not restore datafiles. You can additionally specify the check logical clause to instruct RMAN to check for logical corruption.

RMAN> Restore database validate 

• Verify integrity of backups (Physical corruption)
• By default RMAN checks only for physical corruption when validating. Physical corruption is when the block contents don't match the physical format that oracle expects.

RMAN>  Restore database validate check logical

To check for logical corruption using RMAN


Logical corruption is when the block is in correct format but the contents aren't consistent with what oracle expects.Same info will be reflected in alert.log file & v$database_block_corruption view.RMAN cannot recover logical corrupt blocks.

To recover logically corrupt blocks restore the datafile from a backup and perform media recovery.

When rman can't find a backup piece or detects corruption it will issue a "failover to previous backup" message and automatically searches for a previously taken backup abnd will stop when it finds a good backup or untill it has searched through all known backups without finding a good one