COMPAKTOR Output

When a DASD volume is COMPAKTed, COMPAKTOR prints BEFORE and AFTER maps of the DASD volume on the SYSMAP DD statement. This is true whether you actually COMPAKTed the volume or only simulated COMPAKTion. Along with these detailed maps, which can be suppressed by the MAPS= operand, a summary page for each volume is also printed. At the end of the COMPAKTOR run, a combined summary is printed (on DD SYSSUMM or SYSMAP) giving a two-line summary for each DASD processed, sorted by volume serial number. See COMPAKTOR-Reports for examples of these reports.

Measuring the improvement

To determine how much COMPAKTOR has improved a volume, you can review the summary or the combined summary and compare the BEFORE and AFTER figures for the following fields:

  • NUMBER OF FREE SPACE AREAS - This is a measure of volume fragmentation and is usually smaller after COMPAKTion (larger after RELEASE).
  • NUMBER OF FREE CYLINDERS - This too is a measure of volume fragmentation. This value is usually larger after COMPAKTion.
  • SIZE OF LARGEST FREE AREA, IN TRACKS - Again, a measure of volume fragmentation. Normally, you find a larger contiguous free area after COMPAKTion.
  • NUMBER OF DATASETS WITH 2 OR MORE EXTENTS - This figure tells you how many multi-extent data sets exist on the volume. Almost always less after COMPAKTion.
  • NUMBER OF EMPTY TRACKS IN PS/PO/VSAM DATASETS - This figure is the total number of unused but allocated tracks on a volume. This value is smaller if you have specified operands to release unused space from these data sets.
  • IBM FRAGMENTATION INDEX - This index attempts to show the level of fragmentation on a DASD volume, calculated by an IBM-provided formula using the size of free space areas on the volume. A value of 0.000 is achievable only when there is only a single free area, and values close to 1.000 occur when there are many tiny free areas (such as every other track). The formula is a non-linear function involving natural logarithms and is biased toward most of the free space being collected into one large area. We believe it is difficult to understand and does not always accurately reflect the effect of fragmentation on the ability to allocate data sets; generally, if there are 3 or fewer free areas the fragmentation index should be ignored. We suggest that volumes with indexes over 0.200 or over 20 free space areas should be COMPAKTed, but you may need to run COMPAKTOR simulations on all your volumes to decide what threshold should be used by your installation.

SYSPRINT messages

Several messages in the SYSPRINT DD statement output indicate the amount of work that COMPAKTOR did on each volume:

  • CPK316I shows how many tracks COMPAKTOR actually restored, moved, or released.
  • CPK319I shows how many tracks COMPAKTOR was able to treat as unmovable due to SIZEKEEP= options, allowing you to gauge the effectiveness of SIZEKEEP= (the larger the value, the less work CPK did). If the message is absent, either SIZEKEEP=0 was specified or COMPAKTOR was unable to meet its objective without making all tracks movable.

Unable to improve

There are several conditions under which COMPAKTOR may not be able to improve the condition of a volume:

  • User-specified positioning forced COMPAKTOR to create a more fragmented volume.
  • An excessive number of unmovable data sets may prevent improvement.
  • The volume is already optimally organized. Perhaps you just COMPAKTed it or perhaps there is only one data set on the volume.

If any user-specified data set or VTOC positioning was performed or if any unused tracks were freed, COMPAKTOR goes ahead and COMPAKTs the volume. If not, message CPK556W UNABLE TO IMPROVE is issued and the volume is bypassed (to force COMPAKTion, rerun specifying space release or positioning parameters).

 

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