Managing user data with SMS

SMS allows you to match users’ data characteristics (like data set organization, size, and format) to the characteristics of storage devices, without requiring users to know or to understand the hardware configuration at your site. With SMS, end users can store and retrieve data without being aware of space limitations, device characteristics, or volume serial numbers.

Using SMS, you can define allocation management criteria for the different types of data at your site. The values you specify identify your users’ requirements for space, availability, and performance. You define these values to SMS as:

Data Class: A named list of data set allocation attributes that SMS assigns to a data set when it is created.
Storage Class: A named list of data set storage service attributes that identify performance and availability requirements. SMS uses these attributes to control data placement.
Management Class: A named list of management attributes that SMS uses to control DFSMShsm actions for data set retention, migration, backup, and release of allocated but unused space.
Storage Group: A named list of DASD volumes used for allocation of new SMS-managed data sets or for a dummy storage group.

Automatic class selection (ACS) is the SMS mechanism for assigning SMS classes and storage groups (also known as constructs). Depending on the DFSMSdss command you are using, SMS invokes some or all of the ACS routines in the following order:

Storage class ACS routine
Management class ACS routine
Storage group ACS routine

SMS uses the assigned constructs to automatically place and manage data and storage. For example, you can use a storage class to keep performance-sensitive data on high-speed storage devices and use management classes to control the movement of less active data to tape.

If there are WRITE statements in the SMS ACS routines, these are only displayed in the DFSMSdss output when the ACS routines return a nonzero return code. If DFSMSdss processes a data set successfully, then no WRITE messages are displayed.

Related reading: For more information about SMS, see the ACS routine information in z/OS DFSMSdfp Storage Administration.