MSC VTAM message resynchronization and recovery

For IMS systems linked by VTAM®, IMS maintains the integrity of messages and control blocks during system and session failures. IMS recovers sessions automatically if both half-sessions save resynchronization information.

Because a logical link is broken after an abend caused by a system failure, user action is required for recovery. Performing a normal cold start destroys session resynchronization information, so you should use the /ERESTART command to restart IMS.

During emergency restart, IMS restores the message queues. After the link is reestablished, IMS resynchronizes messages between half-sessions.

In contrast, the message queues are lost during a cold start because IMS cannot restart the link at the point at which the system failed. Messages that were lost must be resubmitted.

After you reestablish a VTAM link after a session fails, you must reassign as primary the half-session originally assigned as primary (the one from which you issue the /RSTART command or the type-2 UPDATE MSLINK(linkname) START(COMM) command).

A z/OS® system can run more than one IMS subsystem at a time. One IMS subsystem communicates with the other subsystem using real-storage-to-real-storage communication. z/OS provides the real-storage-to-real-storage connection primarily for system protection and testing purposes.

If a physical link between systems fails, the MTO should reestablish communication through an alternate physical link:

Use the /MSASSIGN LINK command or the type-2 UPDATE MSLINK(linkname) SET(MSPLINK(msplinkname)) to reassign the logical link to an alternate physical link. This command must be entered on both systems.
Use the /RSTART LINK command or the type-2 UPDATE MSLINK NAME(linkname) START(COMM) command to start the logical link.