2. USAGE GUIDELINES › 2.3 Miscellaneous Usage Notes for All Files › 2.3.2 The Calculation and Importance of DURATION

2.3.2 The Calculation and Importance of DURATION

When VCC obtains an inventory of the DASD and DFHSM
resources on a given day, it stores a timestamp of when
data collection started and places this same timestamp in
every record it produces.  This timestamp becomes known to
CA MICS as the data element called ENDTS.

The next time VCC runs, a new value for ENDTS is necessarily
created.  Each data record produced by VCC will have this
current value of ENDTS and the prior value for ENDTS (this
latter data element is known internally as PREV_TS).

The difference between these two timestamps is stored in the
CA MICS common element called DURATION. While DURATION is an
element common to many information areas in CA MICS, its
definition within the VCA, HSM and HSB information areas is
simply the time between successive inventories of the data.

DURATION is a vitally important data element for these
information areas because of the characteristics of space
occupancy over time versus space occupancy at a given point
in time.  The former measurement is worthy of accounting and
chargeback applications since the space occupied is being
factored by how long the data set has occupied that space.

DURATION provides an efficient method of measuring space
occupancy without incurring the overhead and complexity of
operation associated with "event-driven" techniques such as
capturing every ALLOCATE, EXTEND, PARTIAL-RELEASE, SCRATCH,
and RENAME event from MVS.

DURATION calculations are maintained at the following
"levels" by VCC and brought "forward" to the CA MICS Space
Analyzer components VCA and HSM by including the ENDTS and
PREV_TS timestamps directly in the data records:

    1 - at the VOLSER level
    2 - at the DFHSM control data set level

If VCC processes a VOLSER once per day, the ENDTS and PREV_TS
values for data sets on that volume will yield a DURATION
that approaches 24 hours and we would expect any variance to
be negligible. Yet if, for example, a volume called DATA01 is
EXCLUDED from the production VCC run for one day for some
operational reason, when DATA01 is included again in the
scan, the ENDTS and PREV_TS values in the records produced
for data sets on that volume will be approximately 48 hours.