Q and A

Asked and Answered

I read your column "Time to Reconsider SMS" (Spring 2000), and I agree with you regarding the advantage of defining DB2 user tablespaces under the control of the Storage Management System (SMS). But what about the DB2 Catalog and directory? Can you also define DB2 catalog and directory data sets to be under SMS control?

Robert Catterall responds:

There are two issues to consider here, and they are somewhat interconnected.

First, do you want your DB2 for OS/390 or z/OS data sets to be user-managed or DB2-managed? If they are to be DB2-managed, you would specify USING STOGROUP on a CREATE or ALTER TABLESPACE or INDEX statement.

The second issue has to do with whether or not SMS will be used for DB2 data set location within the disk subsystem. If you want to use SMS in this way for DB2-managed data sets, you would use DB2 STOGROUPs defined with VOLUMES ('*').

The DB2 catalog and directory data sets can't be DB2-managed in the way that user tablespace and index data sets can be. Why? Because you can't create DB2-managed data sets without DB2 STOGROUPs being defined. STOGROUPs can't be defined if a DB2 subsystem isn't installed and operational, and the catalog and directory data sets have to be defined before the DB2 subsystem can be installed and made operational.

The DB2 installation job DSNTIJIN (in the SDSNSAMP partitioned data set that ships with DB2) defines the catalog and directory data sets. These data sets are defined via DEFINE CLUSTER commands in the DSNTIJIN job. DEFINE CLUSTER is a VSAM Access Method Services (AMS) command, and the commands in the DSNTIJIN job can be modified to suit the needs of a particular installation. I expect that you could code an AMS command such that SMS will be used to determine the location of the data sets within the disk subsystem, but I don't know enough about AMS to be certain of that. Even if doing so were a possibility, I'm not sure that I would recommend such a strategy. I believe that hand placement of the DB2 system data sets is advisable, given the importance of these objects.

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