Communication Methods › Configuring DASD Control Files

Configuring DASD Control Files

CA MIM control files must be allocated on a shared DASD device that is accessible to all systems on which CA MIM executes. When a DASD device is shared among systems, remember the following guidelines:

• In z/OS systems, the device must be defined as shared in the SYSGEN IODEVICE macro.
• In z/VM systems, the device must support reserve/release processing. The two types of reserve/release processing are:

  Real reserve/release processing

  Is needed when CA MIM is running on two or more real processors. That is, two or more systems that are not guests under the same z/VM system.

  Virtual reserve/release processing

  Is needed when two or more operating systems operate as guests of z/VM.

  If you have several guests running under one z/VM operating system, and you have at least two real processors in your installation, use both real and virtual reserve/release processing.

Use these guidelines, to configure DASD for your control files as follows:

• Whenever control files are shared by two or more real processors, specify SHARE YES in the system configuration file or SHARED=YES in the HCPRIO ASSEMBLE file for all RDEVICE macros that you are using to define DASD for control files. SHARED=YES or SHARE YES must be specified on each guest system, even if the first-level z/VM system does not share DASD with any other processor or LPAR.

  Note: The SHARED=YES or SHARE YES parameter is required to propagate reserve commands to the DASD hardware and upward to the host z/VM system. For details about the SHARED parameter, see Virtual Machine/Extended Architecture System Product: Planning and Administration (IBM publication number GC23-0378) or the equivalent guide for your system.

• When your installation runs two or more operating systems as z/VM guests on the same real processor, specify virtual reserve/release processing for the minidisks that are used as a control file (whether or not other processors are in use). To do so, specify mode MWV on the MDISK statement in the z/VM directory entry for one of the guest operating systems. Then, using mode MW, issue a link command to the same minidisk from each of the other guest operating systems.

  Using virtual reserve/release processing protects guests on the same real processor from each other. Also, hardware reserve still operates correctly when virtual reserve/release is invoked, thus protecting users in separate real processors from each other.

• Always specify virtual reserve/release processing for the control file minidisks even if there are no guest operating systems under z/VM. Define the minidisk by specifying mode MWV on the MDISK statement. Reserve/release channel commands are not processed correctly unless virtual reserve/release is specified.