How to dynamically change MIM from DASDONLY DSN to XES list structure

Products

• MIM Resource Sharing (MIM)
• MIM Data Sharing (MII)
• MIM Tape Sharing (MIA)
• MIM Message Sharing (MIC)

Issue/Introduction

This document describes how to change the Control File from DASDONLY using Data Sets to using Coupling Facility List Structures (XES) without cycling MIM.

If all systems in a MIMplex are in the same geographic location and DASDONLY is in use, using list structures has some advantages over DASD Data Sets or switching to XCF when running MII:

1. FASTER
2. EASY TO IMPLEMENT - FEW CHANGES REQUIRED
3. EASIER OPERATIONALLY - NO VCF MASTER FLIP FLOP

Note: MIA and MIC do not have the same performance requirements as MII - it is sufficient for them to use a DASD control file. 

Environment

Release : 12.5
Component : MIM

Resolution

The following sections of the MIM documentation may be helpful to read in advance:

 

1. The Programming Guide provides a wealth of information for this in varying locations.
Here is basic information for setting up an XES control file for a new MIMplex

Coupling Facility Structure Control Files (XES)

 

2. Good background information is a comparison of DASD and List Structure here. You can leave COMMUNICATION=DASDONLY.

Comparison of DASD Control Files and Coupling Facility Structure Control Files

 

3. This section shows more detail about the differences between the physical control files

Physical Control Files

 

4. XES Control File placement is described here - it has some good additional displays and information.

How You Allocate Control and Checkpoint Files

 

Following is the procedure to switch from DASD to list structures without shutting down.

NOTE: The XESFILEID needs to be sequentially numbered higher than any existing DASD DDNAMEs.
                     Example: If the MIIINIT shows
                        ALLOCATE DDNAME=MIMTBL00,DSNAME=hlq.CF00  
                        ALLOCATE DDNAME=MIMTBL01,DSNAME=hlq.CF01  
                     The XESFILEID's would need to be 02 and 03.

• Use the ALLOCSTR sample JCL to create 2 new list structures. The size of the primary structure can be determined by the DISPLAY CFSIZE command. The alternate List Structure should be 20% larger than the primary.
  
• Update the XCF POLICY to reflect the 2 new list structures
  
• Enter the MIM ALLOCATE command on all systems:
  • *ALLOCATE XESFILEID=02 STRNAME=mim_primary_structure
  • *ALLOCATE XESFILEID=03 STRNAME=mim_alternate_structure
  • *DISPLAY FILES
    
• Confirm that files 02 and 03 are allocated and usable
  
• If so, use the MIGRATE command to migrate to one of them. The command is global so only needs to be entered on 1 system:
  
  • *MIGRATE CF=02
    
• *DISPLAY FILES
  
• Confirm that 02 is now IN-USE
  
• Optionally you can try to migrate to 03 to confirm its operational.
  
• Comment out or delete the ALLOCATE commands for files 00 and 01 in the init member
  
• Add the following ALLOCATE commands in the init member:
  • ALLOCATE XESFILEID=02,STRNAME=mim_primary_structure
  • ALLOCATE XESFILEID=03,STRNAME=mim_alternate_structure