Advanced Topics › Initial Communication Methods Overview

Initial Communication Methods Overview

The MIMINIT COMMUNICATION parameter allows you to specify which communications method you want CA MIM to use upon startup.

The options include:

1. DASDONLY (Physical) – Instructs CA MIM to use a physical control file (DASD or coupling facility list structure) upon startup. The DASDONLY communication provides the control file on a shared DASD volume or a coupling facility list structure.
   • Benefits
     • Allows the MIMplex systems to be any combination of sysplexed and non-sysplexed images.
     • Solid-State DASD provides a high performance equivalent to CTC communication options.
     • Coupling facility list structures provide high performance.
   • Requirements
     • A 3380/3390-type DASD volume or a coupling facility list structure accessible by all systems participating in the MIMplex.
     • If using coupling facility structure control files are used, all MIMplex systems must be in the same parallel sysplex.
   • Recommendations
     • At least ten cylinders of DASD must be available for a DASD CA MIM control file.
2. CTCDASD (VCF/Physical) – Instructs CA MIM to use the communications method specified by the INITIAL sub-keyword; either CTC or DASD. However, by specifying CTCDASD as the initial communications method, the DASD file is always treated as a backup and recovery will result in a migration to the DASD file.
   • Benefits
     • Allows the MIMplex systems to be any combination of sysplexed and non-sysplexed images.
     • Provides high performance, especially for CA MII sites.
     • Provides backup master system capability in a master system failure.
     • Defines backup DASD or coupling facility structure control file in a CTC failure or if there are no available backup masters.
     • Is not subject to contention delays associated with DASD I/O when VCF is in use.
   • Requirements
     • A 3380/3390-type DASD volume or coupling facility list structure accessible by all systems participating in the MIMplex.
     • 3088 or extended mode ESCON CTC devices connecting at least one system to all others in the MIMplex.
     • At least one CA MIM address space defined to manage the virtual control file (VCF).
3. CTCONLY (VCF) – Instructs CA MIM to use CTC devices for communications upon startup. The CTCONLY communication method has the control file located in virtual storage in a master CA MIM address space and passed from the master to client systems through CTC devices.
   • Benefits
     • Allows the MIMplex systems to be any combination of sysplexed and non-sysplexed images.
     • High performance, especially for CA MII sites.
     • Requires no shared DASD control file.
     • Requires no coupling facility structure control file.
     • Provides backup master system capability in case of master system failure.
     • Is not subject to contention delays associated with DASD I/O.
   • Requirements
     • A 3088 or extended mode ESCON CTC devices connecting at least one system to all others in the MIMplex.
     • At least one CA MIM address space that is defined to manage the virtual control file (VCF).
     • At least one checkpoint file defined on each system in the MIMplex.
4. XCF (VCF) – Instructs CA MIM to use XCF communication upon startup. The z/OS Cross System Coupling Facility (XCF) communication method is similar to CTCONLY; however, the virtual control file (VCF) is passed from the master system to client systems through the XCF.
   • Benefits
     • Provides high performance, especially for CA MII sites.
     • Provides RMF reporting for optimizing XCF signaling and messaging
     • Allows for a backup master system in case of a master system failure.
     • Is not subject to contention delays associated with DASD I/O.
     • Requires no coupling facility structure control file.
     • Requires no shared DASD control file.
     • Automatically discovers connections between CA MIM systems, requiring no additional configuration.
   • Requirements
     • All systems in the MIMplex must be in a single sysplex.
     • At least one CA MIM address space defined to manage the virtual control file (VCF).
     • At least one checkpoint file must be defined on each system in the MIMplex.
     • CA Common Services for z/OS.
5. ICMF - This is a special communication method that can be used to transport transactions to part of the MIMplex. ICMF is used only with the CA MIC component. This method can be used to transmit console messages between z/OS systems that do not communicate with each other through the control file.
6. NONE – This option allows you to start a CA MIM task on a single system without involving any cross-system communication media. This option is used primarily in new installations for pre-production testing.

Although you must specify an initial communications method on the MIMINIT COMMUNICATION parameter, you are not constricted to using that communication method during execution (except for COMMUNICATION=NONE or COMMUNICATION=ICMF). At any time, you can dynamically change communication methods, after correctly configuring an alternate method. For more information, refer to the following scenario documentation: How to Dynamically Change CA MIM Communication Methods.