2. COST ACCOUNTING CONCEPTS FOR IS ORGANIZATIONS › 2.7 DASD/DFHSM/SMS Storage Accounting › 2.7.5 VSAM Accounting

2.7.5 VSAM Accounting

This section gives a brief overview of VSAM.  It explains the
difference between the VCA DAA and _VS files, why the _VS
file used to be required for VSAM accounting, and why the DAA
file is now preferred.

A brief overview of VSAM must limit itself to a very narrow
part of this vast subject.  The most important concepts
related to accounting will be the boundaries of this
discussion.

VSAM was first introduced by IBM in 1974 and has gone through
several transformations since that time.  For our purposes
here, the most significant aspect of VSAM development
occurred in 1981 with IBM's introduction of a completely new
catalog structure called the Integrated Catalog Facility
(ICF) catalog.  The ICF catalog structure gathered acceptance
at an increasingly rapid rate such that today most
enterprises have totally converted to ICF structures.

A significant distinction must therefore be made pertaining
to understanding accounting requirements for VSAM--namely,
what the salient differences are between ICF catalog
structures and the prior VSAM catalog structure which we will
call "old-style VSAM" catalogs.

Old-style VSAM catalogs supported the concept of a
"suballocated data space".  This structure was represented by
a single entry in the VTOC (that is, to MVS allocation
routines, this appeared like one big VSAM data set).  It was
composed of free space and whatever VSAM clusters were
defined within the data space (hence the term
"suballocated").  The contents were only known by examining
the catalog since the VTOC did not contain the "internal
view" that was maintained by VSAM in the catalog.

From an accounting perspective, determining "ownership" from
the VTOC by itself was impossible because the objects in the
data space could belong to many different departments,
divisions, or users.  Again, only the catalog entries would
allow a view into a suballocated data space.
ICF catalog structures require all VSAM data sets to be
"unique" and hence, suballocated VSAM data spaces are not
supported with an ICF catalog.  The main impact of this
implementation for our purposes is that there is now a
one-to-one correspondence between an entry in the VTOC and an
entry in the ICF catalog for a given VSAM data set.  This
means that the VTOC entry for a VSAM data set can be treated
like any other non-VSAM data set for the determination of
space allocated.  The ICF catalog contains the space
management information too, but it is redundant and it is not
the definitive source of information about how much space is
occupied on the volume.  For example, the IDCAMS DELETE
NOSCRATCH function can result in the VTOC becoming
"out-of-sync" with the ICF catalog.  Since such a scenario
still leaves the space allocated on a volume, the VTOC is
clearly the definitive source for accounting purposes.
Likewise, if a data set is SCRATCHED but not uncataloged, the
VTOC will reflect the fact that the space is no longer
allocated.  This allows unique VSAM data sets to be treated
the same as non-VSAM for space allocation accounting.  So
while the ICF catalog will contain many things of interest to
someone pursuing a performance problem or some other esoteric
aspect of VSAM, it is the VTOC that becomes the most
important data source for space allocation accounting
information.

This leads to the conclusion that this relationship can be
exploited to simplify your DASD accounting definitions to a
single source--the VTOC.  If your installation has converted
to ICF catalogs, you should consider accounting for all data
sets, including VSAM, from the VCADAA file that is built from
the VTOC.  The VCA_VS file is constructed from the ICF
catalogs and any "old-style" VSAM catalogs if they exist.
Treating the VCADAA file as the definitive source for
information about space accounting is not only potentially
more accurate but easier to understand since the distinction
between VCADAA and VCA_VS for accounting purposes will no
longer be necessary.

The design of the CA MICS Space Analyzer Option (VCA) is
rooted in support for the suballocated spaces which were
characteristic of the "old-style" VSAM catalogs.  Support for
these old structures is continued in VCC, but most
installations have long since converted to ICF catalogs.  You
can determine if you have "old-style" VSAM catalogs connected
to your systems by examining the output to the VCCSTATS
ddname in a typical production run of VCC in your shop.
Assuming you have only ICF catalogs (see the VCC User Guide
for guidance in interpreting this listing), you should review
your current methods of accounting for VSAM.