Specifying the number of VTOC copies to keep

As DFSMShsm makes a generation of dump copies, it makes a copy of the VTOC of the level 0 volume being dumped for that generation and associates it with the dump copies that are made. DFSMShsm uses the VTOC copy when a dump copy is used to restore a data set. You can specify how many copies of the VTOC are kept. DFSMShsm does not create a VTOC copy when an ML1 volume is dumped.

The example system demonstrates how VTOC copies are kept. It has been stated that storage groups 1 and 2 are using dump classes ONEWEEK and TWOWEEK and that storage groups 3 and 4 are using ONEWEEK and FOURWEEK. Every seven days a new generation is made for all volumes with a copy for dump class ONEWEEK. In addition, every 14 days the volumes in storage groups 1 and 2 are dumped to dump class TWOWEEK so that for those generations, two copies of the volumes in storage groups 1 and 2 are made. However, only one VTOC copy is made for each source volume in a generation even though two copies of the volume are made. Table 1 shows the copies in the various generations for one dump cycle.

In this example, the generation-numbering scheme is not the one used by DFSMShsm but is a simplified scheme for instructional purposes.

Table 1. Generations of Example Dumps
Day	Generation	ONEWEEK	TWOWEEK	Discard VTOC Copy
7	1	X		None
14	2	X	X	None
21	3	X		1
28	4	X	X	None

Now, assuming that you have specified that you want two copies of the VTOC saved for each of dump classes ONEWEEK and TWOWEEK, complete the following actions:

When generation 1 is made, save one VTOC copy for dump class ONEWEEK.
When generation 2 is made, save one VTOC copy for both dump classes ONEWEEK and TWOWEEK.
When generation 3 is made, save one VTOC copy for dump class ONEWEEK and discard the VTOC copy from generation 1 because it exceeds the two VTOCs specified for dump class ONEWEEK.
When generation 4 is made, make one VTOC copy for dump classes ONEWEEK, TWOWEEK, and FOURWEEK; however, the VTOC copy from generation 2 cannot be deleted even though it exceeds the two VTOCs specified for dump class ONEWEEK, because it is still needed to satisfy the two VTOCs specified for dump class TWOWEEK. At this time, you have VTOC copies from generations 2, 3, and 4. The copies for generations 3 and 4 satisfy the two generations for dump class ONEWEEK. The copies for generations 2 and 4 satisfy the two generations for dump class TWOWEEK.

The VTOCCOPIES subparameter of the DUMPCLASS parameter controls the number of VTOC copies kept for the dump class. The dump VTOC copy data sets are written to ML1 volumes. The space required for these data sets varies with the size of the original VTOC, but it is less than that of the original VTOC because only part of each data set VTOC entry is written in the dump VTOC copy.

When no VTOC copy exists for a particular set of dump copies, DFSMShsm can no longer use its automatic search capability to restore data sets from that dump (although it can restore entire volumes). Lack of a VTOC copy also prevents DFSMShsm from providing listings of the data sets contained in that dump. Authorized users can restore data sets from a specified dump volume even though the VTOC copy does not exist.

In the example system, save two VTOC copies for dump classes ONEWEEK and TWOWEEK and no VTOC copy for dump class FOURWEEK. The DUMPCLASS parameters for the DEFINE commands are completed as follows:

DEFINE DUMPCLASS(ONEWEEK AUTOREUSE -
DATASETRESTORE FREQUENCY(7) NORESET -
RETENTIONPERIOD(21) UNIT(ACL) -
VTOCCOPIES(2))
DEFINE DUMPCLASS(TWOWEEK NOAUTOREUSE -
NODATASETRESTORE FREQUENCY(14) -
DISPOSITION('SEND OFFSITE BIWEEKLY') -
NORESET RETENTIONPERIOD(42) -
UNIT(ACL) VTOCCOPIES(2))
DEFINE DUMPCLASS(FOURWEEK NOAUTOREUSE -
NODATASETRESTORE DAY(28) -
DISPOSITION('SEND OFFSITE MONTHLY') -
NORESET RETENTIONPERIOD(84) -
UNIT(ACL) VTOCCOPIES(0))