ACT DFHSM Migrated Data Sets
Data in a DFHSM environment can be conceptualized as pyramidal in shape.
rm
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
MICS Space Analyzer Option
HSM product via the MICS
Space Collection Option. The 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
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 DASD Accounting Features for more information about this subject.