ABCs of z/OS System Programming Volume 3 - IBM Redbooks

5.26 Managing data with a minimal SMS configuration
Device-independence space allocation
System-determined block size
Use ISMF to manage volumes
Use simplified JCL to allocate data sets
Manage expiration date
Establish installation standards and use data class
ACS routine to enforce them
Manage data set allocation
Use PDSE data sets
Figure 5-26 Managing data with minimal SMS configuration
Managing data allocation
After the SMS minimal configuration is active, your installation can exploit SMS capabilities
that give you experience with SMS and help you plan the DFSMS full exploitation with
system-managed data set implementation.
Inefficient space usage and poor data allocation cause problems with space and performance
management. In a DFSMS environment, you can enforce good allocation practices to help
reduce a variety of these problems. The following section highlights how to exploit SMS
capabilities.
Using data classes to standardize data allocation
You can define data classes containing standard data set allocation attributes. Users then
only need to use the appropriate data class names to create standardized data sets. To
override values in the data class definition, they can still provide specific allocation
parameters.
Data classes can be determined from the user-specified value on the DATACLAS parameter
(DD card, TSO Alloc, Dynalloc macro), from a RACF default, or by ACS routines. ACS
routines can also override user-specified or RACF default data classes.
You can override a data class attribute (not the data class itself) using JCL or dynamic
allocation parameters. DFSMS usually does not change values that are explicitly specified,
because doing so alters the original meaning and intent of the allocation. There is an
Chapter 5. System-managed storage 285