Preallocate data sets for SYSMDUMP dumps

You may use any dataset name you wish for the SYSMDUMP dataset. However, the dataset name SYS1.SYSMDPxx will be treated specially. If you use the data set naming convention of SYS1.SYSMDPxx for a DISP=SHR data set, the system writes only the first dump, with all subsequent dump requests receiving system message IEA849I. The data set can be either a magnetic tape unit or a direct access storage device (DASD) data set.

When using this naming convention, you must manage the dump data set to use the same data set repeatedly for SYSMDUMP dumps. For subsequent dumps, you must initialize the SYS1.SYSMDPxx data set with an end-of-file (EOF) mark as the first record.

Naming Convention: You must use SYS1.SYSMDPxx, where xx is 00 through FF and identifies the exact data set to be used.

Data Set Disposition: If you specify DISP=SHR with the SYS1.SYSMDPxx naming convention, the facility that enables the system to write only the first dump becomes active.

If you specify DISP=SHR without the SYS1.SYSMDPxx naming convention, the system writes a new dump over the old dump when the same data set is the target for multiple dumps. This also happens for multiple dumps within the same job if each step does not specify FREE=CLOSE on the SYSMDUMP DD statement.

For dispositions other than DISP=SHR, the system uses the data set as if it were any other MVS™ data set. If you specify DISP=MOD, the system writes the dump following the previous dump, so that the data set contains more than one dump. If you specify DISP=OLD, the system writes a new dump over the old dump when the same data set is the target for multiple dumps.

Data Set Management: To minimize the loss of subsequent dumps, your installation exit should follow these steps for the management of SYS1.SYSMDPxx data sets:
  1. Intercept system message IEA993I. The system issues this message when it writes the dump to the SYS1.SYSMDPxx data set.
  2. Copy the dump onto another data set.
  3. Clear the SYS1.SYSMDPxx data set by writing an EOF mark as the first record, making it available for the next SYSMDUMP dump to be written on the data set.
The installation exit routine can be one of the following:
  • The exit routine specified on the USEREXIT parameter in the MPFLSTxx parmlib member

See z/OS MVS System Messages, Vol 6 (GOS-IEA) for a description of system messages IEA849I and IEA993I. See z/OS MVS Installation Exits for information about the installation exit routine.