5. FILES › 5.2 VTOC/Catalog Activity Information Area Files › 5.2.3 Volume Allocation File (VCAVOA) › 5.2.3.3 VCAVOA Usage Considerations

5.2.3.3 VCAVOA Usage Considerations

This section identifies special considerations and techniques
related to using the VCAVOA file.

Storage Group Name (STORNAME)

STORNAME is set to blank unless the actual storage group name
is captured by VCC at data collection time. Sites that have
implemented volume pooling without DFSMS could use a PROC
FORMAT combined with the _USRSVOA exit point to associate a
VOLSER with a poolname and place it in STORNAME.

Organization of Extent Information

The observations for each volume in the DETAIL timespan of
the Volume Allocation File do not contain variables
describing the size and location of each free space extent.
Instead, each observation contains an array of eight
variables, VOASPF01 through VOASPF08, that are used as free
space buckets.  Each variable contains the count of free
space extents whose lengths fall within the range of space
defined for that variable.  The range for each variable is:

   VOASPF01  -    1 to  100 tracks
   VOASPF02  -  101 to  200 tracks
   VOASPF03  -  201 to  300 tracks
   VOASPF04  -  301 to  400 tracks
   VOASPF05  -  401 to  600 tracks
   VOASPF06  -  601 to  800 tracks
   VOASPF07  -  801 to 1000 tracks
   VOASPF08  - 1001 and over

For example, if the value of VOASPF03 is 13, this means that
the volume has 13 free extents whose sizes are between 201
and 300 tracks in length.

In sharedprefix.MICS.SOURCE, member $VCAMSTR defines a SAS
macro that assigns the value ranges that determine the above
elements. To change these values, you could construct a local
modification to this member, carefully preserving sequence
numbers and following other procedures discussed in the
CA MICS System Modification Guide.

Collecting Only Volume Level Statistics

VCC has a run time parameter called DATAINFO=N which causes
VCC to skip writing records at the data set level (that is,
record segments that would eventually become observations in
the VCADAA and VCA_VS files).  The intent of DATAINFO=N
collection is to provide an easy means of scanning the VTOCs
to obtain various totals (and volume attributes) without
incurring the overhead of writing (and then processing into
CA MICS) the much more voluminous quantities of detail
information about data sets.

Moreover, DATAINFO=N collection suggests the very real
feasibility of scheduling VCC volume-level data gathering as
frequently as every hour or even every 15 minutes for
selected volumes or storage groups for special studies.

With DATAINFO=N data collection, the following elements are
set to missing values because they are only attainable
through the summarization of data from the VCA_VS file:

  VOAVSPSA  VSAM Space Allocated
  VOAVSPAU  VSAM Space Used
  VOAVEXNO  VSAM Extents Allocated
  VOAVEXUS  VSAM Extents Used
  VOAVDSET  VSAM Data Set Count

Various tradeoffs make this acceptable:

o   More important levels of allocation such as VOASPACA
    and capacity such as VOACAPMB are accurate and always
    available.

o   Volume-level only data collection by means of DATAINFO=N
    should be processed in a separate database unit --
    distinctly different in configuration and options from
    the production unit that contains data set level files
    (VCADAA,VCA_VS,HSMMIG,HSBBAC) and Accounting JOURNAL
    files.

o   The audience for this data is probably confined to
    storage administrators and data center management.

Averages from Summarized Data Using VOAVOLNO

Determining the average value of a numeric (accumulated) data
element requires division by a special count data element
called VOAVOLNO.

For example, VOASPACA and other numeric elements are
accumulated.  Therefore, to show the average space allocated
for a month, VOASPACA must be divided by VOAVOLNO. VOAVOLNO
is a count of the number of times VCC scanned the volume
during the month.

In contrast, VOACAPMB (capacity of a volume in megabytes), is
a retained data element and treated as a constant.  Therefore
it's value at the DETAIL timespan is propagated into the
higher timespans during summarization. The capacity of a
VOLSER with a given DEVTYPE is assumed to be constant over
time.

This same principle holds true at the DAYS timespan if VCC
takes an inventory of the volume more than once per day.