Each of the data set description fields of the DCB, except for direct data sets, can be specified when your job is to be run. Also, data set identification and disposition, and device characteristics, can be specified at that time. To allocate a data set, you must specify the data set name and disposition in the DD statement. In the DD statement, you can specify a data class, storage class, and management class, and other JCL keywords. You can specify the classes using the JCL keywords DATACLAS, STORCLAS, and MGMTCLAS. If you do not specify a data class, storage class, or management class, the ACS routines assign classes based on the defaults defined by your storage administrator. Storage class and management class can be assigned only to data sets that are to be system managed.

ACS Routines. Your storage administrator uses the ACS routines to determine which data sets are to be system managed. The valid classes that can either be specified in your DD statement or assigned by the ACS routines are defined in the SMS configuration by your storage administrator. The ACS routines analyze your JCL, and if you specify a class that you are not authorized to use or a class that does not exist, your allocation fails. For more information about specifying data class, storage class, and management class in your DD statement see z/OS MVS JCL User's Guide.

Data Class. Data class can be specified for both system-managed and non-system-managed data sets. It can be specified for both DASD and tape data sets. You can use data class together with the JCL keyword LIKE for tape data sets. This simplifies migration to and from system-managed storage. When you allocate a data set, the ACS routines assign a data class to the data set, either the data class you specify in your DD statement, or the data class defined as the default by your storage administrator. The data set is allocated using the information contained in the assigned data class. See your storage administrator for information on the data classes available to your installation and z/OS DFSMSdfp Storage Administration for more information about allocating system-managed data sets and using SMS classes.

You can override any of the information contained in a data class by specifying the values you want in your DD statement or dynamic allocation. A data class can contain any of the following information.

Related reading: For more information on the JCL keywords that override data class information, see z/OS MVS JCL User's Guide and z/OS MVS JCL Reference.

In a DD statement or dynamic-allocation call, you cannot specify directly through the DSNTYPE value that the data set is to be an extended-format data set.

   //ddname DD DSNAME=NEW.PLI,DISP=(NEW,KEEP)

You cannot specify the keyword DSNTYPE with the keyword RECORG in the JCL DD statement. They are mutually exclusive.