Rule Definition
Use BLOCK CONTAINS 0 allows the operating system to optimize the block size and ensure that the maximum number of records will be processed for a single file input/output operation. Small block sizes increase runtime and larger block sizes reduce runtime.

Remediation
Add a BLOCK CONTAINS 0 clause or set the value to 0 in the file descriptor (FD) to let the system using the most suitable value.

Violation Code Sample

* Example 1 - Block size will not be optimized by system 
       DATA DIVISION.
       FILE SECTION.
       FD FICIN LABEL RECORDS ARE STANDARD.
       01 FICIN-REC PIC X(80).
      * Example 2 - Block size will not be optimized by system
       DATA DIVISION.
       FILE SECTION.
       FD FICIN LABEL RECORDS ARE STANDARD
                      BLOCK CONTAINS 10 RECORDS.
       01 FICIN-REC PIC X(80).
      * Example 3 - Block sizes will be optimized by system
       DATA DIVISION.
       FILE SECTION.
       FD FICIN-1 LABEL RECORDS ARE STANDARD
                  BLOCK CONTAINS 0 RECORDS.
       01 FICIN-1-REC PIC X(80).
       FD FICIN-2 LABEL RECORDS ARE STANDARD
                  BLOCK CONTAINS 0 CHARACTERS.
       01 FICIN-2-REC PIC X(80).
       FD FICIN-3 LABEL RECORDS ARE STANDARD
                  BLOCK CONTAINS 0.
       01 FICIN-3-REC PIC X(80).

Fixed Code Sample

* Example 1
       DATA DIVISION.
       FILE SECTION.
       FD FICIN LABEL RECORDS ARE STANDARD
                BLOCK CONTAINS 0.
       01 FICIN-REC PIC X(80).
      * Example 2
       DATA DIVISION.
       FILE SECTION.
       FD FICIN LABEL RECORDS ARE STANDARD
                BLOCK CONTAINS 0 RECORDS.
       01 FICIN-REC PIC X(80).

IBM Enterprise Cobol for z/OS - Programming Guide