To update a member of a PDS, updated records can either be written back to their original locations, or the entire member (in updated form) may be rewritten as a new member of the data set. In the latter case, the directory entry must be updated to point to the rewritten member.

If a checkpoint is taken before rewriting an entire member, one must also be taken immediately after updating the directory, because the control program deletes the updated directory entry if it repositions the data set for restart from the original checkpoint. Because no entry then points to the original member, the postrestart processing will be unsuccessful.