Generation Data Groups (GDG)

Generation Data Groups (that is, GDG data set groups) are groups of data sets that can all be referred to by a common name. The operating system keeps generations in chronological order. The operating system retains a certain number of generations for each data set, and deletes obsolete generations as necessary.

Each generation of a data set is identified by a suffix that is added to the data set name. The suffix is in the following format:

GxxxxVyy

Where xxxx is a four-digit generation number (0001 through 9999) and yy is a two-digit version number (00 through 99).

For more information, see IBM document DFSMS/MVS USING DATA SETS.

Examples

A.B.C.G0001V00 is generation data set 1, version 0, in generation data group A.B.C.

A.B.C.G0009V01 is generation data set 9, version 1, in generation data group A.B.C.

Control-M/Tape Handling of GDG Data Sets

Control-M/Tape records GDG data sets using their full names (meaning, the GxxxxVyy suffix is included in the data set name). When Control-M/Tape searches for rules to apply to a GDG data set, it first searches for a rule that matches the complete data set name (with the GDG suffix). If no rule matches the data set name with the GDG suffix, Control-M/Tape searches for a rule that matches the data set name without the GDG suffix.

When collecting stacking statistics, Control-M/Tape ignores the GxxxxVyy suffix (meaning, the same statistics are used for all generations of a specific data set).

CYCLE Type Retention and GDG Data Sets

Control-M/Tape can recognize multiple data sets as different versions of the same data set. The criteria for determining if a data set is a new cycle (meaning, generation) of an existing data set, is specified using installation parameter CYCLECNT. Depending on the value specified for this parameter, a cycle may refer to a group of data sets with:

• The same name.
• The same name and the same creation date.
• The same name and the same job name.
• The same name, same creation date, and same job name.

Retention for a data set by Control-M/Tape can be set according to cycle number. For example, if a rule indicates that only 10 cycles of a data set are retained, when the 11th cycle of the data set is created, the oldest cycle (generation) of the data set is automatically expired by the next run of Control-M/Tape retention management utility CTTRTM.

Depending on how a DO RETENTION statement is specified, you can either indicate that only data sets with matching names are considered cycles of the same data set, or all data sets with a specified prefix are considered cycles of the same data set.

Note: Control-M/Tape cycles do not have to consist of GDG data sets. However, if GDG data sets are retained by the CYCLES retention type, Control-M/Tape ignores the GxxxxVyy suffix and recognizes different generations as being of the same data set.