Data set backup and restore

BWO backups are taken at the VSAM sphere level. You can use DFSMShsm or DFSMSdss to take the backup copy. You are recommended to use DFSMShsm because, without DFSMShsm installed, you must supply automatic class selection (ACS) routines to fulfil the SMS requirements for BWO support.

When you use DFSMShsm, you still use DFSMSdss as the data mover. You can specify this using the DFSMShsm SETSYS command: 
SETSYS DATAMOVER(DSS)

The DFSMS processing at the start of backup is dependent on the DFSMS release level. For releases before DFSMS 1.2, DFSMSdss first checks the BWO attributes in the ICF catalog to see if the data set is eligible for BWO. If it is, the backup is made without attempting to obtain exclusive control and serialize updates to this data set.

For DFSMS 1.2 onward, DFSMSdss first tries to obtain exclusive control of the data set. If DFSMSdss succeeds, an enqueued form of backup takes place. If this serialization fails, DFSMSdss checks the BWO attributes in the ICF catalog to see if the data set is eligible for BWO. If it is, a BWO backup is attempted. If it is not eligible, the backup attempt fails.

This change will prevent DFSMS starting a BWO backup after CICS® has abnormally terminated.

At the end of the BWO backup, DFDSS again checks the BWO attributes. If the data set is no longer eligible for BWO, the backup is discarded. Events that cause this situation are:
  • File closing during BWO, which sets the ‘BWO disabled’ state
  • Start of VSAM split, which sets the ‘BWO enabled and VSAM split in progress’ state
  • End of VSAM split, which sets the ‘BWO enabled/disabled and VSAM split occurred’ state.

At the start of a backup, if the state is ‘BWO enabled and VSAM split occurred’, DFSMSdss resets the state to ‘BWO enabled’. Then, if another VSAM split occurs, the backup will be discarded at the end of the backup operation.