JCL DCB Parameter

JCL DISP Parameter JCL SPACE Parameter

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DCB parameter used to create the dataset in JCL.

DCB mainly used to specify the attributes of the dataset. i.e. record length, record format, organization type etc.,

DCB specifies the attributes of the dataset in terms of records.

DCB parameter is mandatory for creating new file from JCL.

DCB parameter is not required for the file created outside of JCL which is referring the file.

Syntax:

	DCB = (LRECL=N,BLKSIZE=YY, RECFM=Z)

DCB mainly uses the below list of keywords for dataset creation

	1. LRECL
	2. BLKSIZE
	3. RECFM
	4. DSORG
	5. BUFNO

LRECL:

LRECL is used to specify the logical record length of the new file.

LRECL be used in two ways based on the records type.

For fixed length records, the same length will be provided in JCL also.

For variable length records, the maximum length record + 4 bytes need to provide in the JCL.

The extra 4 bytes is used to store the length of the record.

Syntax:
	LRECL=N

In the above syntax, N represents the bytes of logical record length.

N value can be in between 1 to 32,760 for non-VSAM data sets.

N value can be in between 1 to 32,761 for KSDS, ESDS and RRDS.

For fixed length files, the bytes would be the normal record length.

For variable length files, the byte would be the maximum record length.

BLKSIZE:

BLKSIZE contains the physical record length.

One block contains one or more logical records in it.

BLKSIZE parameter to specify the maximum length of a block.

This can be used in two ways based on the records type.

For fixed length records, the same length will be provided in JCL also.

For variable length records, the maximum length record length + 8 bytes needs to provide in the JCL.

The first 4 bytes is used to store the length of the record and next 4 bytes is used to store the length of the block.

It is always suggestible to code BLKSIZE as 0, so that the systems can pick up the best.

Syntax:
	BLKSIZE= {value/valueK/valueM/valueG}

Value specifies the size value in Bytes.

ValueK specifies the size value in Kilo bytes.

ValueM specifies the size value in Mega bytes.

ValueG specifies the size value in Giga bytes.

The BLKSIZE can be provided in any format of the above, but the maximum size of the BLKSIZE is 2GB/2047MB.

If the BLKSIZE is not coded, the system will determine the best block size which suits for the requirement.

RECFM:

RECFM specifies the format of the record in the dataset.

RECFM also specifies the characteristics of the record in the dataset.

RECFM is short description for record format.


Syntax:
	RECFM=Z	

In the above syntax, Z represents the format of record fromat.

The various formats are

		Fixed (F)
		Variable (V)
		Undefined (U)
		Fixed Block (FB)
		Variable Block (VB)

U represents undefined length for the records.

F represents fixed length records, unblocked.

FT represents fixed length records, track-overflow feature.

FB represents fixed length records, blocked.

FBA represents fixed length records, blocked and attribute.

FBT represents fixed length records, blocked and track-overflow feature.

V represents variable length records, unblocked.

VT represents variable length records and track-overflow feature.

VB represents variable length records, blocked.

VBA represents variable length records, blocked and attribute.

VBT represents variable length records, blocked and track-overflow feature.

VBS represents variable length, blocked and spanned.

Blocking:

Blocking stores multiple records in single block.

Blocking utilizes best disk space.

Data accessing is fast when Blocking format used.

Unblocked:

Unblocked format stores one record per single block.

Unblocked format not utilizing disk space properly.

Data accessing is too slow when unblocked format used.


If any questions on the above, post your queries on Jcl Discussion forum


JCL DISP Parameter JCL SPACE Parameter

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