Parameters on SYSCHK DD statements

When creating a checkpoint data set:

Code a SPACE parameter, but do not request secondary space.
- The primary space request must be large enough to hold all checkpoints. Although your program or the system can write checkpoints in secondary space, the system cannot perform a restart from checkpoints in secondary space.
- If you do not request secondary space and the primary space fills up, the job abnormally terminates. You can successfully restart the job at the last checkpoint; however, when the processing program or system writes the next checkpoint the job abnormally terminates again.
- If you do request secondary space and the primary space fills up, the processing program or the system writes one invalid checkpoint followed by successful checkpoints. An attempt to restart from one of the checkpoints following the invalid checkpoint results in abnormal termination.
Code the RLSE subparameter of the SPACE parameter only if the processing program opens the checkpoint data set and the checkpoint data set remains open until the end of the program. If you specify RLSE, the system releases unused space after the first CLOSE macro instruction.
Do not code the RLSE subparameter:
- If the processing program opens the checkpoint data set before writing each checkpoint and closes the checkpoint data set after writing each checkpoint. The system releases all unused space while closing the data set after the first checkpoint, leaving no space for additional checkpoints.
- If the system opens the checkpoint data set. The system opens and closes the checkpoint data set before it writes the first checkpoint. With RLSE specified, the system would release all space before the first checkpoint could be written.
Code the CONTIG subparameter of the SPACE parameter to request contiguous space. The system otherwise provides additional primary space using extents. If the extents are not contiguous, any checkpoints in these extents cannot be used for a successful restart.

When retrieving a cataloged checkpoint data set:

Code the DSNAME parameter.
Code the DISP parameter to specify a status of OLD and a disposition of KEEP.
Code the VOLUME parameter. If the checkpoint entry is on a tape volume other than the first volume of the checkpoint data set, code the volume serial number or volume sequence number to identify the correct volume. The serial number of the volume on which a checkpoint entry was written appears in the console message issued after the checkpoint entry is written.
Code the UNIT parameter, if you coded the VOLUME parameter, because the system will not look in the catalog for unit information.

When retrieving a checkpoint data set that is not cataloged:

Code the DSNAME parameter. If the checkpoint data set is a partitioned data set (PDS), do not code a member-name in the DSNAME parameter.
Code the DISP parameter to specify a status of OLD and a disposition of KEEP.
Code the VOLUME parameter. The serial number of the volume on which a checkpoint entry was written appears in the console message issued after the checkpoint entry is written.
Code the UNIT parameter.

Other parameters:

Code the LABEL parameter if the checkpoint data set does not have standard labels.
Code DCB=TRTCH=C if the checkpoint data set is on 7-track magnetic tape with nonstandard labels or no labels.
If the volume containing the checkpoint data set is to be mounted on a JES3-managed device, do not code the DEFER subparameter of the UNIT parameter on the SYSCHK DD statement.

Note: Do not use VSAM for a checkpoint data set, and do not use a partitioned data set extended (PDSE) for a checkpoint data set.