A backup system which can improve reliability of data without sacrificing
availability of a data processing system and a duplicating apparatus
employed in the backup system. The backup system includes a duplicating
apparatus for taking in data in the transfer of the data and codes from a
host apparatus to a storage apparatus and holding the data as duplicated
data, the duplicating apparatus including a code fetching unit to fetch
the codes and hold the fetched codes as duplicated codes, and a data
verifying unit to verify existence or nonexistence of an error in the
data by comparing the taken data and the duplicated data.