Defining data sets

Data sets can be defined to DFSMSrmm automatically when a data set on a volume is opened, or manually using the DFSMSrmm ISPF dialog or RMM ADDDATASET subcommand.

DFSMSrmm cannot record information about a data set if the first data set on the volume has not been defined to it. If a data set other than the first data set on the volume is being defined, any data sets preceding the data set you are adding must already be defined to DFSMSrmm.

When a data set is opened, DFSMSrmm records the:

Data set name
Record format
Date and time the data set was created
Date the data set was last accessed for read and write processing
Expiration date, which is the date that the data set can be considered for deletion.
LASTREF extra days, or NOLASTREF, if the data set is on a volume managed by the EXPDT retention method.
Data class, management class, storage class, and storage group for system-managed data sets

DFSMSrmm automatically records information about each data set on a volume. You can use the DFSMSrmm installation exit EDG_EXIT100 to ensure that DFSMSrmm records information only about the first data set on the volume. Even though you are only requesting that DFSMSrmm records information about the first data set, you can still add information about other data sets on the volume using the RMM ADDDATASET subcommand.