2. COST ACCOUNTING CONCEPTS FOR IS ORGANIZATIONS › 2.7 DASD/DFHSM/SMS Storage Accounting › 2.7.3 DFHSM Migrated Data Sets

2.7.3 DFHSM Migrated Data Sets

Data in a DFHSM environment can be conceptualized as
pyramidal in shape.  This pyramid is meant to convey a
hierarchy of storage ranging from PRIMARY or migration level
0 to migration levels 1 and 2.  For simplicity, we abbreviate
"migration level" to "ML" and thus, it is common practice to
describe data as residing on primary, ML1, or ML2 storage.
Primary is the normal location of data directly accessible by
applications.  When a data set has not been used for some
specified period, HSM migrates it to ML1 storage volumes,
where the data is usually stored in a compacted form and is
not directly accessible.  It can be recalled quickly to
primary storage when needed.  Finally, when installation
thresholds have been reached, HSM will migrate data from ML1
DASD to ML2 storage.  ML2 storage is usually a densely-packed
tape cartridge.


                             /\
                            /  \
                           /    \
                          /      \
                         /        \
                        /  Primary \
                       /____________\
                      /              \
                     /                \
                    /       ML1        \
                   /                    \
                  /______________________\
                 /                        \
                /                          \
               /            ML2             \
              /                              \
             /________________________________\



In a typical DFHSM environment, the amount of data migrated
through the above hierarchy could be presented as the above
pyramid.  For example, if 400 gigabytes of primary storage is
available for active data, then perhaps a much larger
quantity of data is inactive and has been migrated to less
expensive levels of the hierarchy.
Information on migrated data sets (those at ML1 and ML2) is
available from the CA MICS Space Analyzer Option HSM product
via the CA MICS Space Collection Option.  The CA MICS Space
Collector Option (VCC) can optionally collect basic
accounting and capacity planning information about data sets
that have been migrated from standard VTOCs and moved to
compressed locations in the hierarchy of storage managed by
DFHSM.  Locator information about migrated data sets is
stored in the DFHSM Migration Control Data Set (MCDS).  VCC
serves as a "driver" for the collection of data from the
MCDS.

Using the CA MICS Space Analyzer Option HSM and VCA products,
you can establish different pricing for each level of the
storage hierarchy.  Using the pyramid again, you could
conceive a rate structure that reflects the relative cost of
each layer, as shown in the following example:

                             /\
                            /  \
                           / $  \
                          / 0.10 \
                         /  per   \
                        /   Mb/hr  \
                       /____________\
                      /              \
                     /     $0.05      \
                    /       per        \
                   /    megabyte hour   \
                  /______________________\
                 /        $0.002          \
                /           per            \
               /       megabyte hour        \
              /                              \
             /________________________________\


See Section 2.7.7, DASD Accounting Features, for more
information on this subject.