The two DFSMShsm log data sets are called the LOGX data set and the LOGY data set. The names of the data sets are specified in the procedure used to start DFSMShsm and also in the procedure used to print the LOGY data set.
DFSMShsm always writes information in the LOGX data set. When the LOGX data set becomes full, DFSMShsm automatically swaps the two log data sets. You can use the SWAPLOG command to swap the two log data sets. In addition, you can specify the LOGSW=YES parameter on the START DFSMShsm command to cause DFSMShsm to swap the log data sets during DFSMShsm initialization. When the log data sets are swapped, DFSMShsm does the following:
After the DFSMShsm log data sets have been swapped, start the HSMLOG procedure that is supplied with the DFSMShsm licensed program. This procedure normally resides in PARMLIB. The HSMLOG procedure runs the ARCPRLOG program to do an initial formatting of the information in the LOGY data set and to print the log data set. After running the ARCPRLOG program, the HSMLOG procedure deletes the old LOGY data set and reallocates a new LOGY data set. The ARCPRLOG program is also supplied with the DFSMShsm licensed program.
If you do not print the information in the LOGY data set after the log data sets are swapped and a later swap occurs, you do not have a copy of that information because DFSMShsm writes over the old information in the LOGY data set.
The Aggregate backup and recovery support (ABARS) contains additional information about the contents of the DFSMShsm log data sets and how to print information in the DFSMShsm log.