CA Mainframe VM Product Manager - 1.2 : About DASD Management

DASD management is critical to effective data center operation. In a VM environment, users are allocated DASD in the form of virtual disks or minidisks. Minidisks vary in size and usage and can be distributed among many real DASD volumes. These allocations are defined as MDISK statements in the CP source directory. In addition, there are CP-reserved areas on the DASD volumes that are defined outside the CP directory.

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Traditional DASD Management

Traditional DASD management is a time-consuming manual task that requires extensive record keeping and arithmetic calculations. A VM system programmer must identify minidisks that are underused or near capacity, locate free space on the DASD volumes, and reallocate space to use resources most efficiently.

The effectiveness of manual DASD management depends on the accuracy and completeness of the data collected. The information provided by conventional DASD monitoring, mapping, and reporting utilities is often inadequate, making preventive DASD maintenance difficult. Conventional DASD management utilities map user minidisks using only the CP source directory as input data and identify gaps between the minidisks as unallocated areas. Such an analysis is limited because it assumes that the MDISK statements in the directory accurately reflect what is defined on a volume. The analysis may also be inadequate because the unallocated areas it identifies as free space may actually be CP-reserved areas.

In addition to providing inadequate or misleading data, conventional DASD utilities often provide reports that are voluminous, difficult to interpret, and fail to indicate potential minidisk utilization problems. Thus, system programmers often wait until a user has an impending or recurring disk-full condition, then fix it by searching for and reclaiming underused DASD. Meanwhile, both valuable DASD space and system programmer time are wasted. This translates into increased system and personnel costs.

DASD Management with VM DASD Utilities

The VM DASD utilities identify, analyze, and report on the utilization of your VM system resources and allow you to identify and regain control over incongruent DASD allocations. The utilities provide comprehensive reports that indicate potential minidisk problems and provide you with recommendations to improve DASD allocation. These reports give you complete, relevant and accurate statistical data on CP-allocated DASD. The reports allow you to correct problems before they become issues and reduce the time and money you must spend managing your DASD system.

The VM DASD utilities let you do the following:

  1. Reclaim unused DASD
  2. Accurately determine minidisk allocation, distribution, and use
  3. Assess the costs incurred by in-use, underused, and unused minidisks
  4. Monitor the use of component resources
  5. Set thresholds to provide advanced warning of component- and user-minidisk use levels before they become dangerously high
  6. Increase end user awareness of DASD utilization and costs
  7. Postpone the need to purchase additional DASD