Creating (Allocating) a DASD Data Set Using REALLOC

The REALLOC macro builds a parameter list to allocate a new data set. You can code the macro in the execute, DSECT, and list forms, but not in the standard form. The calling program includes the following requirements and options:

Must be APF authorized
Must allocate the volume to this address space and must ensure it stays mounted during the REALLOC function
Must not hold any locks
Can provide the associated parameter list and parameters in storage either above or below 16MB
Can use any storage key
Can run in either supervisor or problem program state
Can be in either 24 or 31-bit addressing mode
Must note that REALLOC does not call RACF® or catalog management
Must note that REALLOC cannot create data sets on SMS-managed volumes (SMS-managed data sets can be created through JCL or dynamic allocation)
Must note that REALLOC cannot create PDSEs, HFS data sets, or extended format data sets
Requires the address of a UCB, not a UCB copy.

In addition, the calling program must provide the REALLOC macro with one or more model DSCBs. You can use the OBTAIN macro to get the DSCBs from other data sets and modify them for the request. DADSM uses these model DSCBs to validate the allocation request, and to construct the DSCBs written to the VTOC for the requested allocation.

The ALLOC parameter for the REALLOC macro defines the allocation request as either absolute (ABS) or movable (MOV).

The requested data set's allocation is not sensitive to its placement on the volume. This is not a reference to the format-1 DSCB bit DS1DSGU (unmovable bit), that can be either on or off in an ALLOC=MOV request's partial DSCB. That is, the data set can subsequently contain location-dependent information.

An absolute request is limited to a single volume with indexed VTOC support. An absolute request provides a set of allocation parameters, a full format-1 or format-8 DSCB, and an optional format-3 DSCB, that describe the space and attributes of the desired data set. An optional format-9 DSCBs can also be provided to pass additional attributes:

Support is provided for, but not limited to, data sets with a user label extent.
The number of extents to be allocated, and their absolute placement on the volume, are defined by the format-1 or format-8 DSCB and one (optional) format-3 DSCB.

For an absolute request, the following checks are performed prior to writing the passed DSCBs. The type of checks depend on the volume for which the REALLOC macro is issued.

For any volume, a passed DSCB format must not describe a format that is not supported. The supported formats in REALLOC processing are 1, 3, 8, or 9.
For an extended address volume, a passed format-1 DSCB must not describe extents that contain cylinder addresses larger than 65,519.
A passed format-1, format-3, or format-8 DSCB must not describe extents that contain cylinder addresses larger than the highest cylinder address of the volume.
For an extended address volume, a passed format-8 DSCB must not describe a data set organization that is not EAS eligible.
For an extended address volume, a passed format-3 or format-8 DSCB must not describe an extent that begins on cylinder address 65519 or lower and that ends on cylinder address 65520 or higher.
For a volume that is not an extended address volume, a passed format-8 or format-9 DSCB is not allowed.

The partial DSCB (mapped by the IECPDSCB macro) consists of the first 106 bytes of a format-1 DSCB followed by 10 bytes in which the primary space request and number of directory blocks are specified.

A movable request is limited to a single volume with or without indexed VTOC support. A movable request provides a set of allocation parameters and a partial DSCB that describe the attributes of the desired data set:

Absolute track allocated data sets are not supported.
The maximum number of extents that can be allocated is determined by the data set organization (PD1DSORG) and the system managed storage indicators (PD1SMSFG) bytes in the partial DSCB.If PD1DSORG indicates a VSAM data set organization, the maximum number of extents is 7257 across multiple volumes, 123 on a single volume.