Master trace lists the same messages that the system saves automatically and permanently in the hardcopy log, but the entries are maintained in a wraparound table, which means that master trace overwrites old entries when the table is full. You can use master trace data in a dump as a substitute for the hardcopy log when the dump contains the required messages. If the master trace table wraps and overwrites the messages related to your problem before you can request a dump, the dump will not contain useful messages.
In this example, the messages pertinent to the problem will be in the master trace data in the dump, since the problem occurred between the time the trace table wrapped and the time the dump was issued.
To print the system-managed data set containing the hardcopy log, use the JESDS parameter of the OUTPUT JCL statement.