General Considerations for Dynamic Data Set Stacking

Before activating the Dynamic Data Set Stacking facility, verify that the parameters relevant to the Dynamic Data Set Stacking facility are set during installation.

In general, Control-M/Tape Dynamic Data Set Stacking facility selects a volume for stacking only if the following conditions are met:

• The DYNSTK parameter is set to Y in the CTTPARM member and a DO STACK=Y statement is specified in a matching rule.
• The job names and data set names of the creating and created jobs have a matching entry in the Stacking Database. If you want to change this criteria (for example, consider all data sets with a specific prefix as the same data set for stacking purposes), you can use the CTTX002 Dynamic Data Set Stacking facility user exit to override the default operation of Control-M/Tape.
• The average size megabytes of the specified data set is read from the appropriate entry in the Stacking Database. If this information cannot be found, stacking cannot continue. To avoid this problem, specify a default size for data sets through the STKDEFSZ parameter in the CTTPARM member.

  The value of the STKDEFSZ installation parameter can optionally be overridden for a data set or group of data sets through a DO STKDEFSZ statement in a Control-M/Tape rule.

• An appropriate volume is found in the Media Database. This volume must be eligible for stacking, have sufficient free space, and belong to the same pool as the data set to be stacked. Depending on the specification for the STKMODE Control-M/Tape parameter, the volume used for stacking may also need to have the same vaulting pattern as the data set to be stacked.

  The search for a suitable volume can be controlled by Exit 10 (Find Stackable Volume) that controls the stacking algorithm. For more information about Exit 10, refer to the CTTX010 member in the IOA SAMPEXIT library.

  The search can be limited to a specific number of volumes through the STKSRCHL parameter in the CTTPARM member or through a DO STKSRCHL statement in a Control-M/Tape rule.

• The data set to be stacked is allocated in a DD statement in the JCL of a job. Control-M/Tape stacks data sets that are allocated dynamically (using SVC 99) only if the STKALCD parameter was set to Y in the CTTPARM member.

  Note: For a more complete list of conditions, considerations and parameters, see the description of stacking in the organization and administration chapter of the Control-M/Tape User Guide.

• Non-scratch (Active) volumes converted to Control-M/Tape from another Tape Management System are considered not eligible for stacking. Stacking is only performed for volumes that were moved from scratch status to non-scratch status (meaning, the first data set was created on the scratch volume) while Control-M/Tape was operational.

  Note: Active volumes converted from the other tape management system can be stacked through the CTTSBD batch stacking utility (described above). For more information see the description of the CTTSBD utility in the Control-M/Tape chapter of the INCONTROL for z/OS Utilities Guide.

The remainder of this section describes how to implement the Dynamic Data Set Stacking facility at your site.