What is the difference between BLKSIZE and LRECL?

BLKSIZE specifies the number of bytes

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Mike Resnick

  • Mar 11th, 2005

LRECL is the Logical RECord Length (or size of the record in bytes.BLKSIZE is the physical size, in bytes, of all the records that are grouped together into a block of records.Both LRECL and BLKSIZE are expressed as bytes.


  • Jun 16th, 2005

LRECL specifies the record length of the dataset

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  • Aug 25th, 2005

Logical record length is the multiplied wth 10 to the value of BLKIZE...it is the mximum memeory allocated to PS or PDS in order to keep the records in a disk...

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  • Sep 8th, 2005

For fixed-length record it's the record length. 
For variable-length record it's the longest record length plus 4-byte for RDF(Record Descriptor Word).

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  • Sep 23rd, 2005

LRECL, Logical record length, indicates the length of a record of the data.

LRECL is determined differently for fixed-length and variable-length records. For fixed-length the LRECL is the length of the record. For variable-length, the LRECL is the length of the longest record in the data set plus 4. (The extra 4 bytes are added to the front of each record to contain the record length).

BLKSIZE, Block Size. Specifies the length of the file?s records; for FB, BLKSIZE is normally a multiple of LRECL. Several records are usually placed together in a block of efficiency.

For fixed-length records, BLKSIZE should be specified an even multiple of the LRECL. Variable-length records contain 4 bytes at the front of each record that  tell how long the record is (n).  In addition, there are another 4 bytes at the   front of each block telling the length of the block (m).


  • Oct 21st, 2005

BLKSIZE refers to the number of records in one block while LRECL refers to the length of a record in bytes.

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  • Oct 22nd, 2005


BLKSIZE specifies the size of memory allocated while defining a cluster or a file.

while LRECL specifies the logical  length of the records in a file or a cluster



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  • Oct 22nd, 2005

BLKSIZE specifies the number of bytes to be used in the block.LRECL in the sense logical record length in bytes.each record will contain this much if bytes depending upon the fixed block or variable bloock size.

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  • Nov 1st, 2005

LRECL: its noting but LOGICAL RECORD LENGTH. What we spicefy here it get appilied to 1 rec length i.e 1 rec contain upto 80 characters maximully if we spcify 80 there.Normally we specify BLKSIZE interms of LRECL to minimize wastege of space.

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  • Nov 4th, 2005

blksize is represent in number of  bytes,multiples of recordsize.

LRECL is size of record length for fixed lengthrecords

for varible records is  size of recordlength+fourbytes 

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sunil kuaar

  • Apr 5th, 2006

lrecl means length of the files record length but blk size means the number of records mvs system will read together when we will issue a read command mvs does not read single record it reads whole block and put it in buffer next time it reads from buffer mvs takes care of all these things

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