Dynamic allocation

The Image Copy utility can dynamically allocate the following data sets.

Data set groups and areas

The Image Copy utility can dynamically allocate the data set group or area if you do not explicitly supply it in the execution JCL.

To perform the allocation, the utility searches for the dynamic allocation (MDA) module corresponding to the data set group or area. It searches for the module in IMSDALIB, MDALIB, DFSRESLB, and STEPLIB (in the listed order) and uses the first MDA module that is found.

If the utility locates the dynamic allocation module, it dynamically allocates the data set group or area according to the information specified in the module.

If the utility cannot locate the dynamic allocation module, it issues an error message and terminates the task that requested the data set group or area.

The utility can dynamically deallocate the data set group or area when processing completes.

Data set disposition

The utility sets the disposition of dynamically allocated data sets as follows:

If the data set already exists, the utility sets the disposition to the equivalent of (OLD,KEEP).
If the data set does not already exist, the utility sets the disposition to the equivalent of (NEW,CATLG).

Warning

If you do not use some method (such as a generation data group or the Data Set Name user exit) to make sure that the data set name for an output image copy is different from the data set name of the previously created output image copy, the utility may overwrite the data set.

Output image copy data sets

The utility can dynamically allocate the output image copy data set if you do not explicitly supply it in the execution JCL.

You can determine the name that is assigned to the data set by using any of the following methods:

You can specify a dynamic allocation model and, as part of the model information, provide a model data set name that includes literal values and substitution variables. For more information, see Using-dynamic-allocation-models.
You can use the Data Set Name user exit (ICP$DSN). For more information, see Using-the-Data-Set-Name-user-exit.
You can allow the utility to determine the data set name by combining default values with the prefix value that you specify. For more information, see Determining-dynamically-allocated-data-set-names.

If the utility finds an existing, cataloged data set that matches the generated name, the new image copy overwrites the existing data set. If an existing data set is not found, the new image copy is written to a new dynamically allocated data set.

The utility can dynamically deallocate the output image copy data set when processing completes.

Output image copy stacks

The utility can dynamically allocate the DD statement used to define a tape volume on which output image copies are stacked if you do not explicitly supply it in the execution JCL. Regardless of how the output stack is allocated, the individual image copy data sets written to the output stack are always dynamically allocated.

Input image copy and change accumulation data sets

Input image copy data sets can be dynamically allocated for the Incremental Image Copy and Copy Image Copy functions; in addition, change accumulation data sets can be dynamically allocated for the Incremental Image Copy function.

To perform the allocations, the utility uses the information recorded in the RECON data sets; therefore, DBRC must be active.

If you define DBRC using the CATDS option, the input image copy or change accumulation data set must be recorded in the system catalog. The utility dynamically allocates the data set using the name recorded in the RECON data sets and the unit and volume information recorded in the system catalog. The unit and volume information recorded in the RECON data set is ignored.

If you define DBRC using the NOCATDS option, all information about the input image copy or change accumulation data set must be recorded in the RECON data sets. The utility dynamically allocates the data set using the name, unit, and volume information recorded in the RECON data sets. Any unit or volume information recorded in the system catalog is ignored.

You can use the DSUNIT keyword to override the unit information recorded in the RECON data sets. When you specify DSUNIT in the GLBL control statement, it applies to both input image copy and change accumulation data sets. When you specify DSUNIT on a GROUP, IIC, AIIC, CIC, or ACIC control statement, it applies only to the input image copy data set. When you specify DSUNIT on an ACCUM control statement, it applies only to the change accumulation data set.

You can use a unit user exit (ICP$UNIT) to supply the unit type specification for uncataloged image copy and change accumulation data sets. You can use this user exit in cases where multiple uncataloged image copy and change accumulation data sets are being used and when some are on tape and others are on disk. See Using-the-Data-Set-Name-user-exit for additional information about this user exit.

You can use the UNITCHK keyword to bypass the validation of unit names.

The utility dynamically deallocates the input image copy and change accumulation data sets when processing completes.

RECON data sets

The RECONn DD statement defi nes the data sets used by DBRC to record recovery information.

RECONn DD statements are optional and not recommended. IMS allocates the RECONs as part of the DBRC sign-on process from the utility and deallocates the RECONs when access is no longer needed.

If the utility JCL does not include RECONn DD statements, normal IMS processing is used to dynamically allocate RECON data sets on behalf of the utility, and the following conditions apply:

If the utility JCL includes an IMSDALIB DD statement, IMS searches for RECON MDA members in IMSDALIB and STEPLIB libraries but does not search MDALIB or DFSRESLB libraries.
If an IMSDALIB DD statement is not included in the JCL but your RECON MDA members reside in an MDALIB library that is specified in the utility JCL, you do not need to change the JCL because IMS finds the MDA members in the MDALIB libraries in this case.
If your RECON MDA members reside in a DFSRESLB library, you must make changes to provide access to the members. DFSRESLB is never searched for RECON MDA members.

BMCICPKF data set, RCUMSGRC data set, and RMGR repository

If the utility job JCL does not contain DD statements that allocate the BMCICPKF encryption data set and the RCUMSGRC message handling data set, the utility searches IMSDALIB, MDALIB, DFSRESLB, and STEPLIB (in the listed order) for MDA members to allocate these data sets dynamically.

If you are using the Recovery Extensions feature, the utility dynamically allocates the Recovery Manager (RMGR) repository from an MDA member (IRMREPDD) that is found in IMSDALIB, MDALIB, DFSRESLB, or STEPLIB.

DBDLIB data sets

The DBD library or libraries needed to obtain database definition modules can be dynamically allocated.

When you omit the IMS DD statement from the executing JCL, the utility dynamically allocates and concatenates the list of libraries specified in a global options module. You must have already created a global options module for this dynamic allocation to take place. See Customizing-after-installation for information about creating global options modules.

PDX

The PDX needed during execution can be dynamically allocated.

When you omit the PDX DD statement from the executing JCL, the utility dynamically allocates the PDX that is specified in the appropriate control statement or global options module. See Customizing-after-installation for information about creating global options modules.