Understanding the Order of Assigned Data Set Attributes

You can select attributes in more than one way with the DEFINE command. Because more than one value for the same attribute can be given, attributes are selected in the following order of precedence:

  1. Explicitly specified attributes
  2. Modeled attributes
  3. DATA CLASS attributes
  4. Access method services command defaults

Model processing is done after automatic class selection (ACS) processing. For this reason, modeled attributes are not available to pass to ACS, and default attribute values can be passed to ACS instead. For example, if you state that recordsize be selected from a modeled data set, the AMS default recordsize of 4089 is passed to ACS instead.

The INDEXED|LINEAR|NONINDEXED|NUMBERED|ZFS parameter is an exception to the attribute selection order. If you do not specify this parameter, the command default (INDEXED) overrides the DATA CLASS attribute.

DATA CLASS define/alter panel has an OVERRIDE SPACE flag which specifies whether DATA CLASS attributes override attributes obtained from other sources (like JCL, AMS control cards, attributes obtained from LIKE=). OVERRIDE SPACE flag has two possible values (YES|NO). The default is 'NO'.

If this flag is set to 'YES', DATA CLASS override will occur. If 'No' is specified, DATA CLASS override not occur. All existing allocations will remain unchanged unless users take deliberate action to modify their DATA CLASS and ACS routines.

The JCL Space subparameters to be overridden (including dynamic allocations such as TSO ALLOCATE) are:
  • Space type (CYL,TRK, Block length, or record length plus AVREC)
  • Primary Quantity
  • Secondary Quantity
  • Directory blocks
The IDCAMS DEFINE space parameters to be overridden are:
  • Cylinders (Primary, Secondary)
  • Tracks (Primary, secondary)
  • Kilobytes (Primary, Secondary)
  • Megabytes (Primary, Secondary)
  • Records (Primary, Secondary)
  • Controlintervalsize (CISIZE DATA)
  • Freespace (CI-percent CA-percent)

AVGREC, AVG VALUE ,PRIMARY, SECONDARY and DIRECTORY must be explicitly specified. ISMF will return a failure reason code if any one of these fields is not explicitly specified. ISMF will prime all these fields with blanks and the user must explicitly set each field to any valid non-blank value.

If RECORG is specified (i.e set to KS, ES, RR or LS), then CISIZE DATA must be explicitly specified. If RECORG is specified and is set to KS then %FREESPACE CI and %FREESPACE CA must also be explicitly specified. ISMF will prime all these fields with blanks and the user must explicitly set each field to any valid non-blank value based on the rules above. '0' is a valid non-blank value for any of these fields.

Note:
  1. PRIMARY SPACE, SECONDARY SPACE, allocation units and directory blocks will all be picked up either from the JCL or from the DATA CLASS to keep with existing logic. The SPACE information in the DATA CLASS must be all inclusive, otherwise jobs may fail or produce unexpected results.
  2. The Model’s Volume Count is passed to the ACS routines and will override the Data Class Volume Count.

For example: If the model data set has one volume and no candidate volumes, the new data set will have one volume and no candidate volumes.

To make this new data set a multi volume data set, you would have to add the dynamic volume count to the data class that the new data set picks up or the model will need to have specified candidate volumes.