2. COST ACCOUNTING CONCEPTS FOR IS ORGANIZATIONS › 2.7 DASD/DFHSM/SMS Storage Accounting › 2.7.1 Permanent DASD Space Accounting

2.7.1 Permanent DASD Space Accounting

Accounting for permanent DASD data sets requires a system to
identify the pertinent data set names and the space allocated
to them.  Then data set ownership is ascertained to identify
the cost center to be charged.  Data set names, standardized
by a data set naming convention, are used to determine
ownership.  VTOC scans usually produce the necessary
information.

VSAM data spaces, however, present a special charging
problem.  At sites that do not run IBM's Integrated Catalog
Facility (ICF), VSAM naming conventions do not use the owner
name in the data space name.  Even when ICF is installed, the
ICF Data in Index Component Name does not typically provide
enough information for billing.

An additional complicating factor of identifying VSAM data
set ownership is that a single VSAM data space may contain
many clusters (data sets), which belong to separate users.
Since VSAM catalogs contain unique entries showing the
standard data set name for each VSAM cluster, the problem can
be avoided by determining VSAM data set allocations by
scanning the VSAM catalogs.

The information for non-VSAM data sets obtained by the VTOC
scan and the information for VSAM data sets obtained from the
VSAM catalog scans provide complete charging information for
permanent DASD data sets.  This combination of VTOC and
catalog scans provides a standard approach for charging.

It is important to optimize the performance of both scans to
minimize operational and overhead problems associated with
gathering the data.
DASD charging uses space units such as volumes, cylinders,
tracks, or bytes of data over a unit of time, such as days,
to produce a charging unit of measure, such as track days
(where one track day is equivalent to occupying one track for
one day).  The charging unit allows the DASD information to
be extracted at varying intervals while keeping the same unit
of reference.  One representative unit of measure is the
megabyte hour, which denotes the occupancy of one million
bytes for one hour.  The use of megabytes provides a
consistent measure that does not vary with device type,
unlike tracks, which are device dependent; the timespan of
hour provides more precision than day or month.  While the
traditional track day qualified by device type is still a
viable unit of measure, it does not allow for as much
flexibility as megabyte hour.  The charging units multiplied
by a rate per unit produce a charge for each data set, which
is billed to the appropriate cost center.

Small data sets present a dilemma when the charge for them is
so small (less than one cent) that it rounds to zero.  Three
alternatives to address this situation involve calculating
the charges on a monthly basis, using a minimum data set
charge, or carrying greater precision in the charge field.

Another important DASD charging consideration is that some
permanent data sets may be used by many cost centers.  The
charges for these shared data sets can be distributed among
multiple cost centers by prorating the cost.  The
installation sets the guidelines for determining how the
charges are to be distributed.

As IBM's System Application Architecture evolves, it may be
more reasonable to assign the cost of shared databases to a
corporate account and view the data bases as a corporate
asset.  Another option may be to recover the cost with access
charges to users.