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© Copyright IBM Corp. 1999 25
Chapter 4. System Managed Storage Concepts and Components
This chapter is designed to familiarize the DB2 database administrator (DBA)
with the concepts and components of system managed storage (SMS). The
following topics are discussed:
• Background
•Evolution
• DFSMS/MVS components
4.1 Background
The continued growth of data requires the need for a more effective and efficient
way of managing both data and the storage on which it resides. SMS was
introduced in 1988 both as a concept and then as a group of products of MVS
1
to
provide a solution for managing disk storage. Based upon user specifications,
SMS can determine data placement, backup, migration, performance and
expiration. The goals of SMS are:
• A reduction in the number of personnel required to manage that data, by
allowing the system to manage as much as possible
• A reduction in labor-intensive related tasks of disk management, by
centralizing control, automating tasks, and providing interactive tools
• A reduction in the necessity for user knowledge of placement, performance,
and space management of data
4.2 Evolution
Although initially a concept, with a small number of products offering limited
functionality, the introduction of DFSMS
2
has provided the functions needed for a
comprehensive storage management subsystem, which provides:
• Management of storage growth
• Improvement of storage utilization
• Centralized control of external storage
• Exploitation of the capabilities of available hardware
• Management of data availability
With each subsequent release of the product, more features have been
introduced that further exploit the concepts of SMS managed data, and this is
likely to continue; for example, advanced functions for all types of VSAM files,
which require the use of the extended addressability (EXT) attribute in the Data
Class. It is therefore important to understand that those customers who have
taken the time and effort to implement an SMS policy ultimately gain more from
DFSMS enhancements than those who have not.
The characteristics of a DB2 system allows for the management of its data by
SMS. However, there are considerations and choices that need to be made to
tailor it to suit the individual customer’s environment. These considerations are
discussed in the following sections.
1
The term MVS (OS/390) refers to the family of products which, when combined, provide a fully integrated operating system.
2
The term DFSMS refers to the family of products which, when combined, provide a system managed storage environment.