DB2 for OS/390 Version 5

Alter Storage Group -- Fields and controls

DMS storage is managed by DB2. Using, DMS, you define the volumes of the storage group. Each volume-id is a volume serial number of a storage volume. It can have a maximum of six characters and is specified as an identifier or a string constant. There is an MVS limit of 59 volumes that can be defined and allocated per data set.

SMS

DFSMSdfp Storage Management Subsystem (SMS) can be used to manage DB2 DASD data sets. These volume identifiers are nonspecific identifiers. SMS uses one volume for each number specified in the Maximum number of volumes field. There is an MVS limit of 59 volumes that can be defined and allocated per data set.

Password

Type a VSAM control or master level password in the form of a short identifier. If the password is a delimited identifier, it can contain any special characters acceptable to access method services. The password is used to access the integrated catalog facility catalog. The password that protects the catalog must be established by the installation of access method services. If this field is not specified, no password is used by DB2 to access the integrated catalog facility catalog.

The password does not apply to data sets managed by DFSMS/MVS's storage management subsystem (SMS). Data sets defined to SMS should be protected by Resource Access Control Facility (RACF) or some similar external security system.

Number of SMS volumes

SMS volumes use nonspecific volume identifiers. You need only to type the maximum number of volumes to define and allocate.

Storage group name

A name for DB2 storage groups is an unqualified identifier of up to eight characters. A DB2 storage group name must not be the same as the name of any other storage group in the DB2 catalog.

The changes you make to the volume list using this ALTER STORAGE GROUP window, have no effect on existing storage. Changes take effect when new objects are defined or when the REORG, RECOVER, or LOAD REPLACE utilities are used on those objects.

All the volumes in a storage group must be of the same type.

A DB2 storage group is a set of volumes on direct access storage devices (DASD). The volumes hold the data sets in which tables and indexes are actually stored. The description of a storage group names the group and identifies its volumes and the VSAM catalog that records the data sets. All volumes of a given storage group must have the same device type. But, parts of a single database can be stored in different storage groups. Try to assign frequently accessed objects (indexes, for instance) to fast devices and seldom used tables to slower devices; that choice of storage groups improves performance.

DFSMS storage groups are not the same as DB2 storage groups.

After you define a storage group, DB2 stores information about it in the DB2 catalog. (This catalog is not the same as the integrated catalog facility catalog that describes DB2 VSAM data sets). The catalog table SYSIBM.SYSSTOGROUP has a row for each storage group and SYSIBM.SYSVOLUMES has a row for each volume. With the proper authorization, you can display the catalog information about DB2 storage groups by using SQL statements

Use storage groups whenever you can, either specifically or by default. However, if you want to maintain closer control over the physical storage of your tables and indexes, you can define and manage your own VSAM data sets using VSAM access method services. Yet another possibility is to have SMS manage some or all of your DB2 data sets.

Storage groups is a list of DASD volumes you specify to hold your DB2 objects. Storage is then allocated from these volumes as your tables are loaded with data.

Integrated catalog facility

For both user-managed and DB2-managed data sets, you need at least one integrated catalog facility catalog, either user or master, created with the integrated catalog facility. You must identify the integrated catalog facility catalog (the "integrated catalog") when you create a storage group or when you create a table space that does not use storage groups.

If your integrated catalog facility catalog is password protected, you must supply a password when you create a storage group. That is the control or master password of the integrated catalog facility catalog that lists all dynamically created data sets in the storage group.

The integrated catalog facility passwords are used by DB2 in access method services DEFINE, ALTER, and DELETE commands. They are stored in the SYSIBM.SYSSTOGROUP table of the DB2 subsystem catalog.

If you change the integrated catalog password known to DB2 in redefining the storage group, you must execute access method services to change that password in the integrated catalog.