REPLACE Tells whether the table space and all its indexes need to be reset to empty before records are loaded. With this option, the newly loaded rows replace all existing rows of all tables in the table space, not just those of the table you are loading.
RESUME Tells whether records are to be loaded into an empty or non-empty table space. For nonsegmented table spaces, space occupied by rows that have been marked as deleted or by rows of dropped tables is not reused.
NO Loads records into an empty table space. If the table space is not empty, and you have not used REPLACE, a message is issued and the utility job step terminates with a job step condition code of 8.
For nonsegmented table spaces containing deleted rows or rows of dropped tables, using the REPLACE keyword provides increased efficiency.