Defining sharing control data sets

VSAM RLS requires sharing control data sets. These are used to maintain data integrity in the sharing environment. The sharing control data set is used sysplex-wide by all the SMSVSAM servers, and is always duplexed.

Two active, and at least one spare, sharing control data sets must be available at all times.

The size of these data sets depends on the number of MVS™ images in the sysplex and on the number of files that are expected to be open concurrently. The z/OS DFSMSdfp Storage Administration Reference manual gives information about calculating the amount of space that is required for the sharing control data sets.

Sharing control data sets are VSAM linear data sets that must be on volumes that have global connectivity. The data sets can have multiple extents, but only on the same volume. You define them using standard techniques for defining data sets. The names must have SYS1.DFPSHCDS as the first and second qualifiers. See the z/OS DFSMSdfp Storage Administration Reference manual for other rules relating to the definition of sharing control data sets.

You must not issue RESERVEs on any volumes that contain sharing control data sets. Convert any such RESERVEs to enqueues.

You can check that the data sets are available to the sysplex with the MVS DISPLAY SMS command, on any MVS image:

D SMS,SHCDS

This command shows the names of the two active data sets and the spare data set as shown in the following example:

Name	Size	%UTIL	Status	Type
ACTIVE1.VP2SS03 7920KB	7920KB	74%	Good	ACTIVE
ACTIVE2.VP2SS03 7920KB	7920KB	74%	Good	ACTIVE
SPARE.VP2SS03 7920KB	7920KB	74%	Good	SPARE

The DISPLAY command shows only the third and fourth qualifiers of the sharing control data set names; the first and second qualifiers are always SYS1.DFPSHCDS.

The first time an SMSVSAM server is started in the sysplex, you vary online the sharing control data sets with this command for the active data sets:

V SMS,SHCDS(shcdsname),NEW

Use this command for the spare data set or data sets.

V SMS,SHCDS(shcdsname),NEWSPARE

for the spare data set (or data sets). The server cannot start properly if you do not issue these commands.