To allow WebSphere Application Server for z/OS to restart on an alternate system, the following prerequisites must be installed on every system (your original system as well as any systems intended for recovery) before reconfiguring the ARM policies to enable peer restart and recovery.
You must also make sure all of the systems, where you might need to perform restart, are part of the same RRS log group.
Installing the prerequisite service updates on all of these systems will not hinder your current running environment if you want to continue to only restart in place. However, if this service is not installed, there is a possibility that the controller will not be able to move back. OTS will attempt to restart on the alternate system and fail. If there are any URs that are unresolved with RRS once this happens, the controller will not be allowed to restart on the home system until RRS is cancelled on the alternate system. For more information on OTS and RRS, see z/OS MVS Programming: Resource Recovery.
If you do not plan to use peer restart and recovery, you do not need to abide by these functional prerequisites. Your system will instead use the restart-in-place function.
In addition to the preceding products, many JTA XAResource Managers can be used to assist in a WebSphere Application Server for z/OS peer restart and recovery. Consult your JTA XAResource Manager's documentation to determine if it supports restarting on an alternate system.
Clients will see a performance impact if the systems are running at capacity. In an attempt to minimize the memory and CPU impact on the alternate system, the enterprise bean and Web containers are not restarted for servers running in peer-restart mode. This means that application servers that are in the state of being recovered will not be able to accept any inbound work.
After the prerequisites are installed, starting a server on a system to which it was not configured implicitly places the server into peer restart and recovery mode. If you configured your XA Partner log to write to a non-shared HFS, or if you are using a JTA XA Resource Manager, you need to perform the following steps before starting a server:
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