To perform a deferred checkpoint/restart, you must provide the data set environment required by the restart job, using conditional dispositions during the original execution.

Dynamically deallocated data sets have the disposition processed as specified at the time of deallocation. Conditional disposition processing is not performed during abend.

The following rules must be adhered to when resubmitting a job for a deferred checkpoint/restart:

1. A RESTART parameter with a checkid subparameter must be coded on the JOB statement.
2. A SYSCHK DD statement must be placed in the job immediately before the first EXEC statement.
3. The EXEC statements in the job must have unique names. (Upon restart, the system searches for the named restart step.)
4. The JCL statements and data in steps preceding or following the restart step can be different from their original forms. However, all backward references must be resolvable.
5. The restart step must have a DD statement corresponding to each DD statement present in the step in the original, and the names of the statements must be the same as they were originally. However, the restart step can contain, in any position, more DD statements than it contained originally. Except as noted in item 9 below. The total number of volumes specified at restart must equal or exceed the number specified at the checkpoint.
6. If a DD statement in the restart step in the original job defined a data set that was open at the checkpoint to be used, the corresponding statement in the restart job must refer to the same data set, and the data set must be on the same volume, and, in general, have the same extents recorded in its DSCB as it did originally. (See the exceptions in the note that follows.) This means no one can use the DEFRAG function of DFSMSdss to consolidate extents. If the data set is multivolume and is processed by the sequential access method (SAM), only the part of the data set on the volume in use at the checkpoint needs to be the same as it was originally.

   Note: The extents can differ as follows:

   • In the DD statement, you can request that additional space be allocated to the data set when the space currently available is exhausted. If space is allocated after a checkpoint is taken, this space is indicated in the DSCB; after restart from the checkpoint, the space is released, and the DSCB contents are changed to what they were at the checkpoint.
   • In the DD statement, you can code RLSE to request that unused space be released when the data set is closed. If the space is released, the DSCB may indicate a reduced extent for the data set when deferred restart at a checkpoint occurs; no space is allocated to replace released space. Space is not released when a data set is open when the step abends, and step termination is followed by automatic restart.

   JCL specified data sets that were dynamically unallocated prior to the checkpoint are not allocated at restart.

   When there is no need to read or modify a data set after restart, the data set can be replaced by a dummy data set if the original data set was processed by SAM and the job step is not restarted from a checkpoint within the data set's end-of-volume exit routine. A VSAM data set using the ISAM interface to VSAM cannot be replaced by a dummy data set. Any dummy data set present at the time of the checkpoint must be present as a dummy data set at restart. Allocation is done for each DD statement in the job step where the checkpoint is taken, even if the data set is closed at the time of the checkpoint.

7. The data in the restart step need not be the same as it was originally. If data following a DD * statement was present originally and is entirely omitted in the restart job, the delimiter (/*) statement following the data may also be omitted. The delimiter statement following a DD DATA statement must not be omitted.
8. The VOL parameter of a DD statement must refer to at least those volumes it refers to at checkpoint time. More volumes may be added if desired. The following DD statement parameters cannot be changed: DISP, DCB, LABEL, and UNIT.
9. Except for the requirements stated in rules 4 through 8, the JCL statements and data in the restart step can be different from their original forms. In particular, the DUMMY parameter can be used for any data that was not open at the checkpoint.
10. If data sets are passed from steps preceding the restart step to steps following it, the DD statements receiving the data sets must entirely define them. They must explicitly specify volume serial number, device type, data set sequence number, and label type, unless this information can be retrieved from the catalog. It is recommended that passed data sets be conditionally cataloged during abnormal termination of the original execution. Label type cannot be retrieved from the catalog.
11. The EXEC statement PGM and COND parameters and the DD statement VOL=REF parameter must not be used in the restart step or in steps following the restart step if they contain values of the form stepname, or stepname.procstepname, referring to a step preceding the restart step.
12. The DD statement VOL=REF parameter is ignored if restart is attempted from a checkpoint taken when the DD statements are opened out of sequence and the referenced DD statement requested nonspecific tape volumes.
13. The volume serial number must be coded on a restart DD for a generation data group if the deferred checkpoint/restart volume serial number list is to be different from the original.