36 Storage Management with DB2 for OS/390
Communications Data Set
The communications data set (COMMDS) holds the name of the ACDS and
provides communicationbetween SMS s ystemsin a multisystem environment.
The COMMDS alsocontains 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 classesassigned to them. These are DataClass, Storage Class,
and Management Class, and theydet ermine thevolume 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. Implementingan SMS Configuration
5.2 Automatic Class Selection Routines
Automatic ClassSelection (ACS) routines are the mechanism for assigning SMS
classes and Storage Groups. Theydet ermine the placement of all new data set
allocations,plus allocations involving the copying, moving, recalling, recovering,
and converting of data sets. ACS routinesare w rittenin ahigh level REXX style
programming language.If SMS is activated, all new data set allocations are
subject to automatic class selection.
There are fourACS routines. Aggregate groups also exist, but for the purposes of
this book are only mentioned where relevant.The ACS routines are executed in
the followingorder:
ALLOCATECONTROL DATASETS
MODIFY ANDCREATE SYS1.PARMLIB MEMBERS
ESTABLISHACCESS TO STORAGE ADMIN ISMFOPTIONS
DEFINEBASE CONFI GURATION
DEFINECLASSES AND STORAGE GROUPS
DEFINEAND TEST ACS ROUTINES
VALIDATEACS ROUTINES AND SMS CONFIGURATION
ACTIVATE SMS CONFIGURATION