Advanced Topics › Communication Methods › Cross-system Communication Methods › Physical Control File Communication Methods › DASD Control Files

DASD Control Files

A DASD control file is a data set that resides on a shared DASD volume used to transport CA MIM transactions throughout the MIMplex. DASD control file communication has the following requirements:

• At least ten cylinders of DASD must be available for the CA MIM control file.
• The DASD volume must be configured as SHARED and accessible by all systems in the MIMplex.

The CA MIM address space on each system contends for access to the control file by issuing hardware reserve requests. Access to the control file is thereby serialized, because only one system has the control file reserved at any given moment.

The DASDONLY communication method may route CA MIM transactions through a DASD control file. The DASD device on which this control file resides must be accessible by all systems participating in the MIMplex. If a coupling facility structure is used, then it must reside on a coupling facility that is accessible by all MIMplex members.

To select the DASDONLY communication method, you must customize certain parameters in the MIMINIT member:

• Define all systems participating in the MIMplex using the DEFSYS statement:

  DEFSYS (sysa,aa,sysa),(sysb,bb,sysb)
  

• Define the DASDONLY communication method on the MIMINIT statement:
• MIMINIT COMMUNICATION=DASDONLY
• Define the control files to be used in the MIMPROC member:

  //MIMTBL00  DD DSN=MIM.CF00
  //MIMTBL01  DD DSN=MIM.CF01
  

• Alternatively, define the control files to be dynamically allocated in the MIMINIT member:

  ALLOCATE DDNAME=MIMTBL00,DSNAME=MIM.CF00
  ALLOCATE DDNAME=MIMTBL01,DSNAME=MIM.CF01
    or
  ALLOCATE XESFILEID=00 STRNAME=MIM#CF00
  ALLOCATE XESFILEID=01 STRNAME=MIM#CF01
  

• Define checkpoint files only if using the ECMF REQUEUE feature.

Important: CA MIM does not support checkpoint files on the high portion of the Extended Address Volume (EAV). If you use EAV, make sure you allocate data sets with EATTR=NO.

Note: For more information, see the Statement and Command Reference Guide.

You may have a combination of both DASD and coupling facility structure control files in a DASDONLY environment.