General Information › Special Considerations › GDG Data Sets and Generation Wrapping

GDG Data Sets and Generation Wrapping

Catalog processing for GDGs turns on the Wrap Bit to create generations from 10,001 to 10,999. The Wrap Bit is then turned off to create generations 1000 and above. This is true for all supported releases of DFSMS.

The Archive, Restore, Delete, Move, Copy, and Sequential Migrate functions have the potential to catalog a GDG by its absolute name. Nearly all of the catalog actions for GDG data sets complete with no alteration of the sequence of generations. The original catalog status is maintained when using RECATMIG set to Y. When RECATMIG is not set to Y, only the active GDGs can be maintained (see sysparm GDGRECAT for other options). The GDG sphere sequence could also be altered incorrectly due to a Wrap Bit when a GDG is cataloged as a new entry.

The Wrap Bits rules Catalog processing uses are as follows:

• Only the generations in the range 0xxx can have the Wrap Bit on.
• The generations in the range 1001–8999 can never have the Wrap Bit on and do not cause the Wrap Bit to be turned on for new generations.
• If there are any generations in the range 9xxx, new generations in the range 0xxx can have the Wrap Bit turned on at creation time.
• If there are generations with the Wrap Bit on and other generations with the Wrap Bit off, creating generation 1000 fails .
• If all of the generations cataloged have the Wrap Bit on, uncataloging the last generation in the range 9xxx causes the Wrap Bits to be turned off, .
• Catalog processing strictly maintains the Wrap Bit. The Wrap Bit cannot be explicitly set, reset, or read.

Example:

• GDS List 1
  • LABS.DSN.LIST.G0002V00
  • LABS.DSN.LIST.G0003V00
  • LABS.DSN.LIST.G0005V00
  • LABS.DSN.LIST.G0099V00
  • LABS.DSN.LIST.G9005V00

  All of these can be archived and recataloged without any problem.

• GDS List 2 SMS
  • LABS.DSN.LIST.G0002V00, Rolled off
  • LABS.DSN.LIST.G0003V00, Rolled off
  • LABS.DSN.LIST.G0004V00, Active
  • LABS.DSN.LIST.G0005V00, Active
  • LABS.DSN.LIST.G0006V00, Active
  • LABS.DSN.LIST.G0007V00, Active
  • LABS.DSN.LIST.G0008V00, Active
  • LABS.DSN.LIST.G0009V00, Deferred

  All of these can be archived and recataloged without a problem while using RECATMIG Y. For RECATMIG N, the rolled off and deferred generations are handled as specified by the sysparm GDGRECAT.

• GDS List 3 Non-SMS
  • LABS.DSN.LIST.G0001V00
  • LABS.DSN.LIST.G0002V00
  • LABS.DSN.LIST.G0003V00
  • LABS.DSN.LIST.G0004V00
  • LABS.DSN.LIST.G0005V00
  • With LABS.DSN.LIST.G9999V00 uncataloged

  If LABS.DSN.LIST.G9999V00 is archived and cataloged, it would become the most current generation regardless of the true sequence. See the GDGRECAT sysparm.

• GDS List 4
  • LABS.DSN.LIST.G0002V00 on volume TSO001
  • LABS.DSN.LIST.G0003V00 on volume TSO001
  • LABS.DSN.LIST.G0005V00 cataloged to ARCIVE
  • LABS.DSN.LIST.G0006V00 on volume TSO001
  • LABS.DSN.LIST.G0007V00 on volume TSO001

  LABS.DSN.LIST.G0005V00 can be safely restored.

• GDS List 5 where the GDG base is defined with a limit of 5
  • LABS.DSN.LIST.G0003V00 cataloged to MIGRAT
  • LABS.DSN.LIST.G0004V00 cataloged to MIGRAT
  • LABS.DSN.LIST.G0005V00 cataloged to MIGRAT
  • LABS.DSN.LIST.G0006V00 cataloged to MIGRAT
  • LABS.DSN.LIST.G0007V00 cataloged to MIGRAT
• List of DSNINDEX records
  • LABS.DSN.LIST.G0001V00, create date 01/01/12
  • LABS.DSN.LIST.G0002V00, create date 02/01/12
  • LABS.DSN.LIST.G0003V00, create date 03/01/12
  • LABS.DSN.LIST.G0004V00, create date 04/01/12
  • LABS.DSN.LIST.G0005V00, create date 05/01/12
  • LABS.DSN.LIST.G0006V00, create date 06/01/12
  • LABS.DSN.LIST.G0007V00, create date 07/01/12

  Generations 0003 -0007 would be selected for recovery as the sphere is full.

Important! Review the RECATMIG, GDGRECAT, and ENQGDGBY sysparms. Because CA Disk uses absolute names to allocate and catalog GDGs, set the ENQGDGBY sysparm to N unless you are using JES3. To avoid potential data set loss, set the GDGRECAT sysparm to N. Review the use of CREATE for Restore. Create date is another factor that is used at restore time to determine generation sequence. If an older generation is restored with a new creation date and later re-archived, it can be selected for recovery out of sequence later.