Fallback considerations

Major functions of IMS are generally not compatible with earlier versions.

Consider the following guidelines when preparing your migration fallback plan. This information is a guide to fallback inhibitors, and is not comprehensive:

• If your IMS system uses ACB libraries, the ACB Maintenance utility (ACBGEN) is required.
• For each IMS that you are migrating to a pre-15.4 level, complete the following steps:
  1. Ensure that the status of all databases and PSBs updated by IMS 15.4 are correct.
  2. Resolve DBRC issues. See DBRC fallback considerations.
  3. Shut down IMS 15.4.
  4. Install the version of IMS that you want.
  5. Cold start the IMS.
• You can use the IBM® IMS Queue Control Facility for z/OS® (QCF) to re-queue IMS 15 messages to IMS Version 13 or IMS 14 message queues.

If you are falling back from an IMS 15.4 system to a prior release in IMS 15, you do not need cold start the system. You can shut down and warm start the system instead.