Specifying how DFSMShsm should respond to a data set in use

To ensure integrity and consistency of the data in a backup version, DFSMShsm tries to serialize on system resources to indicate whether a data set is in use. This prevents the data set from changing while DFSMShsm is backing it up. However, accepting the philosophy that something is better than nothing, you may still want backup copies of data sets that are in use at the time of backup, so long as you can identify (if you should need to recover from such a backup) that a given backup was created while the data set was possibly being changed.

If DFSMShsm makes an unserialized backup, after first trying and failing to serialize on system resources, the data-set-changed indicator remains on; the data set is still eligible to be backed up. If DFSMShsm is configured not to serialize on system resources on the first attempt to back up a data set, the data-set-changed indicator is turned off. The instruction for no serialization is an option of the ARCHBACK user macro and the ARCBDEXT installation exit. However, the ARCINBAK inline backup program always specifies this option, because it expects the JCL to perform its own serialization.

DFSMShsm recognizes two situations involving backup and a data set being in use. First, there are data sets that you do not expect to be open for update, but that may be in use when backup is attempted. For this situation, the SETSYS BACKUP parameter has an INUSE subparameter to control how DFSMShsm can try a second time, after a specified delay, to serialize on a data set before backing it up, and whether successful serialization for such a retry is required or merely preferable. The backups that the INUSE subparameter allows may be placed temporarily on ML1 DASD.

SETSYS BACKUP(INUSE(RETRY(Y) DELAY(10) +
                       SERIALIZATION(PREFERRED)))

For the second situation, there are data sets (typically a database) that you expect to be open for update most of the time. You can use the data set backup installation exit ARCBDEXT for additional control, to direct DFSMShsm either not to serialize before making a backup or to back up the data set even if serialization fails. The SETSYS INUSE subparameters can also apply in this situation, but the exit can override them for a given data set.