Operating Systems

The user directory in z/VM is the repository of all the virtual machines capable of using the system. It’s comprised of several statements that define each virtual machine, including the amount of storage it can use, which disk areas are available for allocation, security properties, virtual switch connections, spooling capabilities, and other device attachment.

There are two ways to do directory management: the XEDIT method, in which the primary administrator edits a large file, and the directory manager method, where an application package is in charge of the directory and provides an interface to manage it.

Consider the first method. In this file, perhaps several thousand to tens of thousands of lines of data are the statements that compose the directory entries for each virtual machine. The XEDIT method of directory management is error-prone. Simple mistakes can cause catastrophic problems and potential data loss. Also, this method requires that disk allocation be performed manually. The administrator must know the availability of open disk areas and point new allocations to them. Careful planning is needed; good disk mapping utilities are available, but the actual process of entering the data into the directory remains manual.

This article focuses on the second method, using a directory manager, and specifically examines the setup and use of z/VM Dirmaint.

Dirmaint is a CMS application that runs in a virtual machine. Its primary purpose to manage the directory on a z/VM system. It’s a priced, optional component that’s pre-installed by the z/VM installation procedure. To use Dirmaint, it must be licensed, enabled, and configured.

Dirmaint provides several interfaces:

  • A command interface is the most prevalent. Several commands have fill-in-the-blank screens.
  • A REXX interface can be used to drive Dirmaint from within the VM system.
  • The Systems Management Application Programming Interface (SMAPI) can be used to invoke Dirmaint functions from within or outside VM.

Dirmaint Advantages

Dirmaint is installed and maintained with regular z/VM maintenance; there’s no separate maintenance process. Recommended Service Upgrade (RSU) and Corrective (COR) service work the same with Dirmaint as with other z/VM components.

A CMS command-level interface lets you send commands to Dirmaint; the Dirmaint commands are designed to mostly mimic directory statements.

A significant benefit of Dirmaint involves automatic disk allocation. When disk space is required for a virtual machine, determine how much is needed (in cylinders or blocks), then point to a volume or group (a pre-determined collection of volumes). Dirmaint will find the space; you don’t need to keep track of open disk areas.

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