ACT 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.
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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 as 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 as the distinction between VCADAA and VCA_VS for accounting purposes will no longer be necessary.
The design of the
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 documentation for guidance in interpreting this listing), you should review your current methods of accounting for VSAM.