It is the disk limit, which is the amount of space the flash recovery area is permitted to use. The minimum size of the Flash Recovery Area should be at least large enough to contain archive logs that have not been copied to tape.
Note: This value does not include certain kinds of disk overhead:
-Block 0 or the OS block header of each Oracle file is not included in this size, so make sure to allow an extra 10% for this data when computing the actual disk usage required for the Flash Recovery Area.
This initialization parameter is a valid destination to create the Flash Recovery Area. The destination can be defined as a directory, file system, or ASM disk group.
Note1: The Flash Recovery Area cannot be stored on a raw file system.
Note2 : DB_RECOVERY_FILE_DEST_SIZE must be set before DB_RECOVERY_FILE_DEST.