Increasing data checks performed by RMAN with "check logical" switch
By default RMAN checks for physical corruptions in data files when performing backups. For a logical check you can add “check logical” to your rman backup command. With this clause rman also checks the block integrity logically.
A few examples how to use it:
backup validate check logical database; backup check logical database; backup check logical incremental level 0 filesperset 4 database;
Checking for both logical and physical corruptions requires the init.ora parameter “db_block_checksum” set to “true” which is also the default. This parameter forces oracle to calculate a checksum for the block before writing it to disk. Doing logical checks with rman has a slight performance overhead when doing backups – typically 1 to 10 percent.
It is not recommended to turn this off for performance reasons bercause the performance overhead is minimal (< 2%) and you will be unable to detect corruptions!