To allocate a new data set using JCL, specify DISP=(NEW,CATLG,DELETE). If the application program completes normally, the data set is cataloged, but if the application program fails, the data set is deleted. All system-managed data sets are automatically cataloged, even if you use a disposition of KEEP.
To update an existing data set, specify a DISP value of OLD, MOD, or SHR. Do not use DISP=SHR while updating a sequential data set unless you have some other means of serialization because you might lose data.
To share a data set during access, specify a DISP value of SHR. If a DISP value of NEW, OLD, or MOD is specified, the data set cannot be shared.
Tip: If SMS is active and a new data set is a type that SMS can manage, it is impossible to determine if the data set will be system-managed based solely on the JCL because an ACS routine can assign a storage class to any data set.