If your program has a DCB and opens the checkpoint data set for output, the checkpoint routine writes a checkpoint entry at the data set's current position and does not close the data set. A user-opened checkpoint data set does not have to be closed after taking the last checkpoint for the job step. All the checkpoint entries are saved in this case, without specifying DISP=MOD. This provides the ability to request a deferred restart from any of the checkpoints.

• Sequential data sets

  For sequential data sets, DISP=OLD, NEW, or MOD has no effect on how the checkpoint entries are written on the checkpoint data set. The first time each checkpoint data set is used, the checkpoint entry is written at the beginning of the file. Each following checkpoint entry is written after the previous entry.

• PDSs

  PDSs are treated in the same manner as unopened DCBs passed to checkpoint.