If a data set has a management class that specifies automatic backup, migration, or transitions, then you must direct the data set to storage groups that are eligible to be processed for automatic backup or migration capabilities.
A generation data group (GDG) is a group of related cataloged data sets that have sequentially ordered names. SMS uses GDG-related information in the management class definition to manage the storage associated with these data sets. Some management criteria is specified in the definition of the GDG. Some management criteria might be specified by assigning a management class to each individual generation in the GDG. Generation data sets within the same GDG might have different management classes assigned by JCL.
DFSMSrmm uses management class names, instead of attributes, for tape data set retention and movement. It matches a management class name with a DFSMSrmm vital record specification (VRS) and implements the policies defined in the VRS.