Those of you who have looked at the CD releases on z/OS will be aware that they don’t support backwards migration. That means that you can take a 9.1.0 z/OS queue manager and migrate it forwards to 9.1.1, but once you have started the queue manager up you can’t go back to 9.1.0. Backwards migration remains fully supported between LTS releases.
There is code in the queue manager which detects when it is about to be migrated from LTS to CD, and tries to prevent an accidental migration. In the 9.0.x CD releases this was done using OPMODE, but as of 9.1.0 OPMODE is no longer an option. So from 9.1.1 the queue manager will issue a WTOR, with message id CSQY041D, when it detects migration from LTS to CD. The user must then respond with a Y to continue migration, or an N to prevent migration and terminate the queue manager.
The screenshot below shows an example of this:
Note that you won’t get this WTOR when going from CD to CD release, e.g from 9.0.5 to 9.1.1, or from LTS to LTS release.