Allocating a new data set under SMS, using the ACS routines defined by your storage administrator, is easier than without SMS. With SMS it is unnecessary to specify the UNIT, VOL=SER, SPACE, or the DCB parameters in the DD statement. For this allocation to succeed, the ACS routines must select a data class that defines the space and data set attributes required by the application.

You can request the name of the data class, storage class, and management class in the JCL DD statement. However, in most cases, the ACS routines pick the classes needed for the data set.

Allocating a PDSE. The DSNTYPE parameter determines if the data set is allocated as a PDSE or as a PDS. A DSNTYPE of LIBRARY causes the data set to be a PDSE. The DSNTYPE parameter can be specified in the JCL DD statement, the data class, or the system default, or by using the JCL LIKE keyword to refer to an existing PDSE.

If the SPACE parameter is omitted in the DD statement, it must be supplied by the data class. You can omit STORCLAS and DATACLAS in the DD statement if the default storage class and data class contain the data set attributes you want. A PDSE also can be allocated using access method services.

When first allocated, the PDSE is neither a program library or a data library. If the first member written, by either the binder or by IEBCOPY, is a program object, the library becomes a program library and remains such until the last member has been deleted. If the first member written is not a program object, then the PDSE becomes a data library. Program objects and other types of data cannot be mixed in the same PDSE library.

Allocating an Extended-Format Data Set. Extended format data sets must be system-managed. The mechanism for requesting extended format is through the SMS data class DSNTYPE=EXT parameter and subparameters R (required) or P (preferred). The storage administrator can specify R to ensure the data set is extended. Then, for VSAM data sets the storage administrator can set the extended addressability attribute to Y to request extended addressability.

Extended format can also be requested using the DSNTYPE parameter on the JCL DD statement, with values of EXTREQ (required) or EXTPREF (preferred). The DSNTYPE specified on a JCL DD statement overrides any DSNTYPE set for the data class.

In addition to a DSNTYPE of EXTENDED, COMPACTION=YES in a data class definition must be specified if you want to request allocation of an extended format data set in the compressed format. A compressed data set can be created using the LIKE keyword on the DD statement and not just through a data class.

Allocating a Large Format Data Set. Large format data sets are sequential data sets that can grow beyond 65 535 tracks (4369 cylinders) up to 16,777,215 tracks per volume. Large format data sets can be system-managed or not. You can allocate a large format data set using the DSNTYPE=LARGE parameter on the DD statement, dynamic allocation (SVC 99), TSO/E ALLOCATE, or the access method services ALLOCATE command. The SMS data class can also provide the DSNTYPE value of LARGE, if the data set does not have another DSNTYPE specified or a DSORG value other than PS or PSU.

Allocating a VSAM Data Set. Starting in z/OS® V2R1, the DEFINE via IDCAMS or JCL for a SMS managed VSAM LDS with a DATACLAS that specifies EA = 'Y' but no Extended Format setting, will be successful. The EA setting in the DATACLAS will be ignored if no EF setting is found for the data set. Informational message IGD17170I will be issued in both cases in the joblog. See z/OS MVS System Messages, Vol 8 (IEF-IGD), z/OS MVS System Messages, Vol 8 (IEF-IGD) for more information on message IGD17170I.