Implementing DB2 storage groups

A storage group is a set of storage objects on which DB2® for z/OS® data can be stored. DB2 uses storage groups to allocate storage for table spaces and indexes, and to define, extend, alter, and delete VSAM data sets.

You have the following options for creating storage groups and managing DB2 data sets:

You can let DB2 manage the data sets. This option means less work for DB2 database administrators.
You can let SMS manage some or all of the data sets, either when you use DB2 storage groups or when you use data sets that you have defined yourself. This option offers a reduced workload for DB2 database administrators and storage administrators. For more information, see Enabling SMS to control DB2 storage groups.
You can define and manage your own data sets using VSAM Access Method Services. This option gives you the most control over the physical storage of tables and indexes.

Advantages of storage groups
Allowing DB2 to manage your data sets by using DB2 storage groups offers several advantages.
Creating DB2 storage groups
You can create DB2 storage groups by using the CREATE STOGROUP statement. DB2 storage groups are a set of volumes on disks that hold the data sets in which tables and indexes are stored.
Enabling SMS to control DB2 storage groups
Managing data sets with the Storage Management Subsystem (SMS) family of products can reduce workload for database administrators and storage administrators.
Deferring allocation of DB2-managed data sets
When you execute a CREATE TABLESPACE statement with the USING STOGROUP clause, DB2 generally defines the necessary VSAM data sets for the table space. However, you might want to define a table space without immediately allocating the associated data sets.
How DB2 extends data sets
When a data set is created, DB2 allocates a primary allocation space on a volume that has available space and that is specified in the DB2 storage group. Any extension to a data set always gets a secondary allocation space.
DB2 space allocation
Primary and secondary space allocation sizes are the main factors that affect the amount of disk space that DB2 uses.
Managing DB2 data sets with DFSMShsm
You can use the Hierarchical Storage Management functional component (DFSMShsm) of DFSMS to manage space and data availability among the storage devices in your system.
Managing your own data sets
You might choose to manage your own VSAM data sets for several reasons.
Defining index space storage
Generally, the CREATE INDEX statement creates an index space in the same DB2 database that contains the table on which the index is defined, even if you defer building the index.
Creating EA-enabled table spaces and index spaces
DFSMS has an extended-addressability function, which is necessary to create data sets that are larger than 4 GB. Therefore, the term for page sets that are enabled for extended addressability is EA-enabled.

Parent topic: Implementing your database design

Related tasks:

Altering DB2 storage groups