The CTCONLY initial communication method uses a control file located in virtual storage (VCF) of the master CA MIM address space. The control file is passed from master to client using CTC devices.
When using CTC devices to communicate, the MIMplex can consist of sysplexed and non-sysplexed images. No shared DASD or coupling facility structure control file is required.
The CTCONLY communication method passes a virtual control file (VCF) on demand from a selected master system to client systems. The VCF is passed between systems using 3088 or ESCON CTC devices that are allocated to the CA MIM address space on each system. You can define the CTC devices using either of the following methods:
Conceptually, a CTC device connects an I/O address on one processor to an I/O address on another processor. VCF data that is sent from one side is received on the other side, so every transmission consists of two operations:
Data can be transmitted in either direction over a CTC path, but it travels only in one direction at any one moment.
We recommend that sites using the CTCONLY communication method are configured symmetrically. For example, every system in the MIMplex should have a CTC path available to every other system, so that multiple systems are eligible as master systems. This redundancy provides the best recovery options.
Note: Although you may have specified CTCONLY as your initial communication method, CA MIM will automatically join an XCF group. CA MIM will build XCF communication paths for all other active members of the CA MIM XCF group. You can instruct each client system to use an XCF path to the master system (if available) by setting your VCFPREFERENCE.
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