# Attribute derivation and definition

This section clarifies the concepts and values associated with specific attributes.

Percent used and free
  - Percent Used and Free for PDS, PDSE, and HFS data sets is calculated based on the allocated and used tracks from the VTOC, and does not take into account internal usage or wastage within the data set.
  - Tracks Used is set equal to Tracks Allocated for PDSE and HFS data sets.
  - For VSAM data sets Percent Used and Free is based on the volume-level High Used and High Allocated RBAs (relative byte addresses).
Space values
  The following details govern the collection and display of space values in the product:
  - Within the Dataset Attributes Database reports and queries, all space values are displayed as Tracks, Megabytes or Gigabytes. By default, the space unit for all delivered Views is Tracks. The default space value columns can be changed as follows:
    1. Modify the Filters tab of the Properties dialog box for the workspace.
    2. Save the workspace under a new name.
    Note: Refer to the IBM® Tivoli® Monitoring: User's Guide to learn how to display alternate columns in a predefined workspace.
  - Megabytes are defined as `1024*1024`. Gigabytes are defined as `1024*1024*1024`.
  - All calculated megabyte and gigabyte values are calculated from the underlying byte totals, and are rounded up.
  - Space values in summary reports for multivolume data sets are for the portion of the data set located on the indicated volume.
  - The Dataset Detail workspace lists all individual pieces of a multivolume data set (assuming that all volumes on which it is located were processed during collection and selected by the Query).
  - Tracks allocated/used
    - Tracks Allocated is always the sum of all tracks in all extents on the volume from the DSCB.
    - Tracks used for non-VSAM data sets comes from DS1LSTAR in the DSCB.
    - Tracks used for VSAM data sets is calculated as follows:

          High Used RBA on the volumes/(VSAM physical record size) *
          (VSAM physical records per track)

      That value is then used to calculate Percent Used and Percent Free and to calculate the total megabytes and gigabytes used.
      Note: Other utilities such as DCOLLECT might assume that VSAM data sets are either 100% Used or 100% Free. If you are comparing aggregate results between utilities (for example, with enterprise-wide space values) be aware that the OMEGAMON® calculation is intended to give a more accurate picture of space usage within VSAM data sets.
  - The SYS1.HASPACE data set (also called the JES2 spool) is always assumed to be 100% Used (`Space Used=Space Allocated`).
Catalog Values
  The following details pertain to catalog values in the product:
  - The VTOC Index (`SYS1.VTOCIX.Vnnnnnn`) and VVDS (`SYS1.VVDS.nnnnnn`) are not included in the Uncataloged Summary.
  - Because the Dataset Attribute database is built starting at the Volume level, there might be entries in a Catalog that are not represented in the Catalog Detail display. The entries that are not displayed can include the following:
    - Data sets that are in the catalog but do not physically exist on any volume
    - Tape data sets
    - VSAM Clusters that do not physically exist on disk
    - Datasets that are cataloged in more than one catalog