COBOL: Blocked and unblocked files

If the creating program lacks a file blocking statement the dataset is created with no record blocking (i.e. FIXED)!!


FD  CRBREDL                               
    BLOCK CONTAINS 0 RECORDS  ---> If omitted causes BLKSIZE=F            
    LABEL RECORD IS STANDARD              
    RECORDING MODE IS F.                  
01  CRBREDL-REC                 PIC X(43).


From the IBM manual, "Enterprise COBOL for Z/OS"


"In a COBOL program, you can establish the size of a physical record with the BLOCK CONTAINS clause. If you do not use this clause, the compiler assumes that the records are NOT blocked. Blocking QSAM files on disk can enhance processing speed and minimize storage requirements."  

	SPACE (cyls)	EXCPS (number of I/Os)	# Records	CLOCK TIME (minutes)
Unblocked (LRECL=43)	2588	4142000	1107944	149.2
Blocked at half-track (standard)	183	1061000	1250200	73.3
Savings	93% reduction	74% reduction	13% increase	51% reduction

Huge space and clock savings in spite of 13% increase in volume.