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© Copyright IBM Corp. 1999 11
Chapter 3. DB2 Storage Objects
This chapter represents an introduction to DB2 for OS/390 (DB2 throughout this
redbook) for the storage administrators interested in understanding the different
types of data related objects used in a DB2 environment. Special emphasis is
placed on the data sets managed directly by DB2.
3.1 DB2 Overview
DB2 is a database management system based on the relational data model.
Many customers use DB2 for applications which require good performance
and/or high availability for large amounts of data. This data is stored in data sets
directly associated to DB2 table spaces and distributed across DB2 databases.
Data in table spaces is often accessed through indexes; indexes are stored in
index spaces.
Data table spaces can be divided into two groups: system table spaces and user
table spaces. Both of these have identical data attributes. The difference is that
system table spaces are required to control and manage the DB2 subsystem and
the user data. The consequence of this is that system table spaces require the
highest availability and some special consideration. User data cannot be
accessed without system data or with obsolete system data.
In addition to the data table spaces, DB2 requires a group of traditional data sets,
not associated to table spaces, that are used by DB2 in order to provide the
appropriate high level of data availability, the back-up and recovery data sets.
Proper management of these data sets is required to achieve this objective.
In summary, the three main data set types in a DB2 subsystem are:
1. DB2 back-up and recovery data sets
2. DB2 system table spaces
3. DB2 user table spaces
3.2 DB2 Data Objects
DB2 manages data by associating it to a set of DB2 objects. These objects are
logical objects. Some of these objects have a physical representation on storage
devices. The DB2 data objects are:
•TABLE
•TABLESPACE
• INDEX
• INDEXSPACE
• DATABASE
• STOGROUP
A complete description of all DB2 objects and their implementation can be found
in the DB2 for OS/390 Administration Guide, SC26-8957, in Section 2. Designing
a database.