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OPTBLKSZ—set optimum block size (used with Allocation)

The OPTBLKSZ function forces the use of a user-specified block size for data sets on DASD and tape.

The most common use of this function is to override hardcoded values for the block size that exists in either JCL or program code. Another common use of this function is to have it assign a block size of 0 to data sets. This function can also be used to assign any block size to a data set.

In general, avoid coding hardcoded values for block size in JCL or program code and let either an SMS data class or the OPTBLKSZ function assign a block size of 0 when you create a new data set. SMS will then assign a block size that is optimal for the device that is being used. Should the data set move to a different device type, SMS can reassign a different block size that is optimal for the new device without the need for JCL or program modifications.

OPTBLKSZ has the following forms:

  • Standard—The standard form of OPTBLKSZ is used to override hardcoded block size values that are specified in JCL or programs on newly created data sets.
  • Enhanced—The enhanced form of OPTBLKSZ is used to override hardcoded block size values that are specified in JCL or programs on both new and existing data sets. OPTBLKSZ can also be used to change the record format. The enhanced form incurs more overhead than the standard form because of the additional processing that is performed during OPEN processing.

For more information, see:



 

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