Module 7: JCL GDG

JCL- Advantages of GDG

Without GDG	Using GDG
Before each run, you need to change the name of the backup dataset in JCL Example:- Initial job ran on July created backup in PS file:- PAYROLL.SALARY.MONTHLY.JULY Now for AUGUST month we can’t use same JCL, thus modification needed in JCL to use dataset:- PAYROLL.SALARY.MONTHLY.AUGUST	No need to change JCL between runs. Only need to specify:- PAYROLL.SALARY.MONTHLY(+1) Which will create PAYROLL.SALARY.MONTHLY.G0001V00 in July and PAYROLL.SALARY.MONTHLY.G0002V00 in August
Keeping track of dataset names is very difficult as we have to manually remember	It will maintain all generations of data sets thus making it easy for us to refer any generations
Need to manually delete older backup data sets	It will delete/uncatalog older generations automatically

All dataset belonging to a GDG must have same DCB parameters such as record length, record format and so on.
Maximum of 255 dataset can exist within a GDG
GDGs must be cataloged
Generations of GDG should be sequential and must reside on disk or tape
For all new generation data sets, DISP parameter must be set to CATLG
For all new generation data sets, DSN and UNIT parameter must be coded