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DD Statement - new data set notes

This page describes how DD statements can be used to allocate new data sets to be kept beyond the life of a job.

The focus here is on the LRECL=, RECFM=, and BLKSIZE= operands, which although not directly related to resource allocation, they will affect capacity and performance.

Writing individual records to a device restricts that devices capacity, and has an adverse effect on a programs performance. It is best practice, wherever possible, to group individual records into blocks, which are then written to the device.

Devices may have BLKSIZE limits, i.e. for disks it is 32760 bytes.

DD Statement - new permanent data set narrative

DSN=, UNIT=. SPACE=

These were discussed on earlier slides.

DISP=

NEW is the default data set status hence the leading comma. If the job is successful the data set will be kept and catalogued. If the job ABENDS, the data set will be deleted.

LRECL=, RECFM=, BLKSIZE=

Unlike on a PC, most traditional data set types are known as record format, and the system needs to know the size of each record (LRECL), whether the records are fixed in size or variable in size (RECFM), and the size of groups of records to be written (BLKSIZE).

This information may be optional as it could be hard coded within a program, in which case valid values in the JCL will be ignored.

For input data sets the information can be retrieved from the data set label.