4. Defining physical data sets
You can automatically delete and redefine database data sets as part of the recovery process by using data set definitions from either the original data set characteristics or the environmental control statement data set characteristics specification. You should first try to use the original data set characteristics to do so.
Use DISP(OLD | NEW) on the DBDSLnnn keyword to identify whether your database data sets will be deleted and redefined. Use the DATRB() keyword on the ADD command to specify the attributes for deleting and redefining database data sets.
If you do not want to use automatic DELETE and DEFINE, but you do not want to reallocate data sets, you must delete and define physical data sets outside of IMS Database Recovery Facility.
When you do not need to change the data set attributes or location for OSAM data sets, those data sets can simply be overwritten without your having to be delete and reallocate them.
DISP(NEW) in IMS Database Recovery
Facility to
automatically delete and redefine database data sets, or delete and redefine database data sets
in another job or step before running IMS Database Recovery
Facility. Any
attempt to perform a recovery using an existing multi-volume OSAM data set containing data
produces unpredictable results.The IMS Database Recovery Facility uses the VSAM REUSE parameter when you specify the DEFINE CLUSTER command. If the database has been allocated with the VSAM REUSE parameter on the DEFINE CLUSTER command, the physical data sets need not be empty in order for the recovery to work.
For VSAM data sets, if you want recovery to run without deleting and redefining the VSAM clusters, you must specify the REUSE parameter.
There are many reasons that you might want to reallocate data sets. For example:
- Changing SPACE parameters.
- Changing VOLUME parameters.
- Changing FREESPACE parameters.
You also need to delete and reallocate if you want to change any of the physical characteristics of the data sets.