Using the Storage Management Subsystem

This topic covers the following subtopics.

Topic
Using Automatic Class Selection Routines
Allocating Data Sets

When you allocate or define a data set to use SMS, you specify your data set requirements by using a data class, a storage class, and a management class. Typically, you do not need to specify these classes because a storage administrator has set up automatic class selection (ACS) routines to determine which classes to use for a data set.

Descriptions of the classes follow:

A data class is a named list of data set allocation and space attributes that SMS assigns to a data set when it is allocated. You can also use a data class with a non-system-managed data set.
A storage class is a named list of data set service or performance objectives that SMS uses to identify performance and availability requirements for data sets. The object access method (OAM) uses storage classes to control the placement of objects in an object storage hierarchy. Each data set has a storage class if and only if the data set is SMS-managed.
A management class is a named list of management attributes that DFSMShsm uses to control action for retention, migration, backup, and release of allocated but unused space in data sets. OAM uses management classes to control action for the retention, backup, and class transition of objects in an object storage hierarchy. DFSMSrmm can use the management class name assigned to a tape data set to identify a policy which should be used to manage the data set. For non-system-managed tape data sets, DFSMSrmm calls the management class ACS routine. See z/OS DFSMSrmm Implementation and Customization Guide.

Your storage administrator defines the attributes of each class in an SMS configuration. An SMS configuration is a complete set of definitions, ACS routines, and other system information SMS uses to manage your data sets. The definitions group data sets according to common characteristics. As you allocate new data sets, the ACS routines assign those characteristics. With the information contained in the SMS configuration, SMS manages your data sets most effectively with a knowledgeable use of the available hardware. See z/OS DFSMSdfp Storage Administration for information about using SMS classes and managing data sets and volumes.

The Storage Management Subsystem (SMS) can manage tape data sets on native volumes in a tape library and on the logical volumes in a Virtual Tape Server (VTS). DFSMSrmm provides some services for the stacked volumes contained in a Virtual Tape Server. See z/OS DFSMSrmm Implementation and Customization Guide.

Some requirements for using SMS follow:

Extended-format data sets and compressed-format data sets must be system managed.
SMS must be active when you allocate a new data set to be SMS managed.
Your storage administrator must be aware that ACS routines are used for data sets created with distributed file manager (DFM). These data sets must be system managed. If the storage class ACS routine does not assign a storage class, distributed file manager deletes the just-created data set, because distributed file manager does not create non-system-managed data sets. Distributed file manager does, however, access non-system-managed data sets.

Table 1 lists the storage management functions and products you can use with system-managed and non-system-managed data sets. For details, see z/OS DFSMSdfp Storage Administration.

Table 1. Data set activity for non-system-managed and system-managed data sets
Activity Allocation	Non-System-Managed Data	System-Managed Data
Data placement	JCL, storage pools	ACS, storage groups
Allocation control	Software user installation exits	ACS
Allocation authorization, definition	RACF³, JCL, IDCAMS, TSO/E, DYNALLOC	RACF³, data class, JCL, IDCAMS, TSO/E, DYNALLOC
Access:
Access authorization	RACF³	RACF³
Read/write performance, availability	Manual placement, JCL, DFSMSdss¹, DFSMShsm²	Management and storage class
Access method access to UNIX byte stream	JCL (PATH=) or dynamic allocation equivalent	JCL (PATH=) or dynamic allocation equivalent
Space Management:
Backup	DFSMShsm², DFSMSdss¹, utilities	Management class
Expiration	JCL	Management class
Release unused space	DFSMSdss¹, JCL	Management class, JCL
Deletion	DFSMShsm², JCL, utilities	Management class, JCL
Migration	DFSMShsm²	Data and management class, JCL
Notes: DFSMSdss: Moves data (dump, restore, copy, and move) between volumes on DASD devices, manages space, and converts data sets or volumes to SMS control. See z/OS DFSMSdss Storage Administration for information about using DFSMSdss. DFSMShsm: Manages space, migrates data, and backs up data through SMS classes and groups. See z/OS DFSMShsm Managing Your Own Data for information about using DFSMShsm. RACF: Controls access to data sets and use of system facilities.

The following types of data sets cannot be system managed:

Data sets having the same name as an already cataloged data set
DASD data sets not cataloged
Unmovable data sets (DSORG is xxU) except when set by a checkpoint function
Data sets with absolute track allocations (ABSTR value for SPACE parameter on DD statement)
Tape data sets
Spooled data sets

Direct data sets (BDAM) can be system-managed but if a program uses OPTCD=A, the program might become dependent on where the data set is on the disk. For example, the program might record the cylinder and head numbers in a data set. Such a data set should not be migrated or moved. You can specify a management class that prevents automatic migration.

Tape volumes in a system-managed tape library can be managed as system-managed storage classes.