Allocating Data Sets

Allocation has two related meanings:

Setting aside DASD space for a new data set.
Connecting a program to a new or existing data set or to a device.
The program can then use the DD name to issue an OPEN macro and use an access method to read or write data.

In this information we often use the term “creation” to refer to the first meaning of “allocation” although creation often includes the meaning of writing data into the data set.

To allocate a new data set on DASD, you can use any of the following methods:

JCL DD statements. See z/OS MVS JCL Reference.
Access method services ALLOCATE command or DEFINE command. See z/OS DFSMS Access Method Services Commands for the syntax and more examples.
TSO ALLOCATE command. See z/OS TSO/E Command Reference for the syntax and more examples.
DYNALLOC macro using the SVC 99 parameter list. See z/OS MVS Programming: Authorized Assembler Services Guide.

There are two ways to cause a new data set to be system-managed:

Specify the SMS parameter STORCLAS explicitly. You can also specify MGMTCLAS and DATACLAS.
Let the ACS routines assign the SMS classes to the data set.

To allocate non-system-managed data sets, you can specify the DATACLAS parameter. Do not specify the MGMTCLAS and STORCLAS parameters.