Dynamic definition for MODBLKS resources fallback considerations

You can fall back from an IMS system that has dynamic definition (DRD) enabled for MODBLKS resources to an earlier version of IMS.

To fall back from an IMS 15 system that uses the IMS repository function to an IMS 14 or IMS Version 13 system that uses a resource definition data set (RDDS):

  1. Ensure that you have a non-system RDDS that contains a complete set of all the resource definitions before shutting down IMS 15.
  2. Cold start the IMS 14 or IMS Version 13 system and import the resource definitions from the RDDS.

To fall back from an IMS system that has DRD enabled and uses an RDDS to an IMS system that does not use DRD:

  1. Ensure that the IMS.MODBLKS data set has a complete set of all the resource definitions while you have DRD enabled. This set of resource definitions includes resource definitions that were originally in the IMS.MODBLKS data set at cold start time, and the resource definitions (or removal thereof) for the resources that were added, changed, or deleted dynamically. Having this set enables you to fall back to using online change for the IMS.MODBLKS data set with all the resources that were defined either by system definition originally or dynamically.

    Optionally, you can use the Resource Definition Data Set (RDDS) Extraction utility (DFSURDD0) to extract the resource definitions to create Stage-1 macro statements from the stored resource definitions in an RDDS.

  2. Shut down IMS normally.
  3. Remove or change the MODBLKS keyword to enable online change for the IMS.MODBLKS data set:
    • Remove the MODBLKS keyword from the DFSCGxxx member or the DFSDFxxx member of the IMS.PROCLIB data set (or from both members).

      If both members are defined, any values specified in the DFSCGxxx member override the values specified in the DFSDFxxx member.

    • Change the value of the MODBLKS keyword from DYN to OLC in the DFSCGxxx member or in the <COMMON_SERVICE_LAYER> section of the DFSDFxxx member of the IMS.PROCLIB data set (or in both members).
  4. Ensure that the IMS JCL includes the MODBLKS DD statement.
  5. Cold start IMS. An IMS cold start creates runtime resource definitions from the stored resource definitions in the IMS.MODBLKS data set. The online change process for the IMS.MODBLKS data set is now enabled. Variations of the dynamic resource definition CREATE, DELETE, and UPDATE commands that change definitions are no longer permitted.
  6. Reinstitute your in-house procedures that use the online change process for the IMS.MODBLKS data set and disable the procedures that use DRD commands.
  7. Perform other pertinent tasks related to falling back to a previous version.