OPTBLKSZ standard form usage notes

OPTBLKSZ provides services for new DASD and tape data sets with record formats of undefined, variable, fixed, or fixed blocked.

The function does not operate on ISAM, direct, or VSAM data sets. The data set allocation must be specified with both record length and a blocked record format (FB, VB, FBA, and so on); without these two pieces of information, a block size is not assigned.

Related topic

OPTBLKSZ—set optimum block size (used with Allocation)

If a BLKSIZE parameter is not specified in a rule, the selected data set is ignored.

If the LRECL of the selected data set is zero or is larger than the rule-specified block size (SET BLKSIZE=), OPTBLKSZ takes no action. For fixed data sets, the rule-specified block size is adjusted to the next lower multiple of the LRECL.

Important

A block size of zero can be specified to request a system-assigned block size; in this case, OPTBLKSZ sets the BLKSIZE to 0. z/OS System-Determined Block Size (SDB) must be driven to reset the BLKSIZE to the optimum value. For SDB to reset the value, the data set must be opened in the same job step in which it is allocated (see NOCATLG2—prevent NOT CATLGD 2 errors (used with Allocation)).

 

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