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36 Storage Management with DB2 for OS/390
Communications Data Set
The communications data set (COMMDS) holds the name of the ACDS and
provides communication between SMS systems in a multisystem environment.
The COMMDS also contains statistics on the SMS, and MVS status for each SMS
volume, including space.
5.1.2 Class and Storage Group Definitions
The storage management policies are defined to the system by use of classes.
Data sets have classes assigned to them. These are Data Class, Storage Class,
and Management Class, and they determine the volume allocation which forms
the Storage Group. The classes manage the data sets, and the Storage Groups
manage the volumes on which the data sets reside.
Figure 11 on page 36 shows the steps taken by an installation to implement an
active SMS configuration.
Figure 11. Implementing an SMS Configuration
5.2 Automatic Class Selection Routines
Automatic Class Selection (ACS) routines are the mechanism for assigning SMS
classes and Storage Groups. They determine the placement of all new data set
allocations, plus allocations involving the copying, moving, recalling, recovering,
and converting of data sets. ACS routines are written in a high level REXX style
programming language. If SMS is activated, all new data set allocations are
subject to automatic class selection.
There are four ACS routines. Aggregate groups also exist, but for the purposes of
this book are only mentioned where relevant. The ACS routines are executed in
the following order:
ALLOCATE CONTROL DATASETS
MODIFY AND CREATE SYS1.PARMLIB MEMBERS
ESTABLISH ACCESS TO STORAGE ADMIN ISMF OPTIONS
DEFINE BASE CONFIGURATION
DEFINE CLASSES AND STORAGE GROUPS
DEFINE AND TEST ACS ROUTINES
VALIDATE ACS ROUTINES AND SMS CONFIGURATION
ACTIVATE SMS CONFIGURATION