This chapter gives a brief overview of Data Facility Storage Management Subsystem (DFSMS) and its primary functions in the z/OS® operating system. DFSMS comprises a suite of related data and storage management products for the z/OS system. DFSMS is an operating environment that helps automate and centralize the management of storage based on the policies that your installation defines for availability, performance, space, and security. The heart of DFSMS is the Storage Management Subsystem (SMS). Using SMS, the storage administrator defines policies that automate the management of storage and hardware devices. These policies describe data allocation characteristics, performance and availability goals, backup and retention requirements, and storage requirements for the system.