Allocating a COMMDS

The following access method services job allocates a 1-track COMMDS;

  //STEP  EXEC PGM=IDCAMS
  //SYSUDUMP DD SYSOUT=*
  //SYSPRINT DD SYSOUT=*
  //SYSIN    DD *
    DEFINE CLUSTER(NAME(SMS.COMMDS1.COMMDS) LINEAR VOL(SMSVOL) -
    TRK(1 1) SHAREOPTIONS(3,3)) -
    DATA(NAME(SMS.COMMDS1.COMMDS.DATA))
  /*

This job creates a VSAM linear data set named SMS.COMMDS1.COMMDS.

The COMMDS must reside on a shared volume accessible from all systems in the SMS complex. To ease recovery in case of failure, the COMMDS should reside on a different volume than the ACDS. Also, you should allocate a spare COMMDS on a different shared volume. z/OS DFSMSdfp Storage Administration provides additional information on the backup and recovery of control data sets. The control data set (ACDS or COMMDS) must reside on a volume that is not reserved by other systems for a long period of time because the control data set (ACDS or COMMDS) must be available to access for SMS processing to continue.

Recommendation: Use SHAREOPTIONS(3,3) when allocating an ACDS. This allows full authority to read from and write to an ACDS from any system. The ACDS and COMMDS must be accessed from all systems in the complex simultaneously.