Interview Questions

DD statement

BLKSIZE parameter

Parameter Type

Keyword, optional

Purpose

Code the BLKSIZE parameter to specify the maximum length of a block. BLKSIZE= {value}

1.Syntax

BLKSIZE= {value}
         {valueK}
         {valueM}
         {valueG}

2.Subparameter Definition

value
Specifies the maximum length, in bytes, of a block.

The number of bytes that you specify for BLKSIZE depends on the device type and the record format for the data set. The maximum is 32,760 for DASD data sets and 2,147,483,648 for tape, except for data sets on magnetic tape with ISO/ANSI Version 3 labels, where the minimum value for BLKSIZE is 18 bytes and the maximum is 2048 bytes. To allow a block size greater than 2048, use installation exit routine IFG0193G.

valueK
Specifies the maximum length, in kilobytes, of a block. (1 kilobyte = 1024 bytes.) The maximum is 2097152. If you code 2097152K, the block size is the maximum: 2,147,483,648 bytes.

valueM
Specifies the maximum length, in megabytes, of a block. (1 megabyte = 1024 kilobytes.) The maximum is 2048. If you code 2048M, the block size is the maximum: 2,147,483,648 bytes.

valueG
Specifies the maximum length, in gigabytes, of a block. (1 gigabyte = 1024 megabytes.) The maximum is 2G. If you code 2G, the block size assigned is the maximum: 2,147,483,648 bytes.

3.Defaults
If you do not code BLKSIZE, the system can, under certain conditions, determine an optimum block size. For detailed information about system-determined block size.

4.Overrides
If you code a non-zero value for the BLKSIZE subparameter on a DCB or DCBE macro instruction or on a DD statement that defines an existing data set with standard labels, the DCB or DCBE BLKSIZE overrides the block size specified in the label.

5.Relationship to Other Control Statements
Do not code the BLKSIZE parameter with the DCB subparameter BUFSIZE. If you code BLKSIZE it will have no effect on EXCP processing unless the application takes special steps to use it.

6.Coexistence Considerations
Not all programs and operating systems prior to z/OS can read blocks longer than 32,760 bytes. For example, Version 2 Release 10 is the first release of OS/390 that can read such long blocks using standard access methods.

7.Examples of the BLKSIZE Parameter

//DD1B     DD     DSNAME=EVER,DISP=(NEW,KEEP),UNIT=3380,
//                RECFM=FB,LRECL=326,BLKSIZE=23472,
//                SPACE=(23472,(200,40))

DD statement DD1B defines a new data set named EVER on a 3380. The DD keywords RECFM, LRECL, and BLKSIZE contain the information necessary to complete the data control block.

//DD2B     DD    DSNAME=NEVER,DISP=(NEW,KEEP),UNIT=3590,
//               RECFM=FB,LRECL=256,BLKSIZE=204K

DD statement DD2B defines a new data set named NEVER on a 3590. The DD keywords RECFM, LRECL, and BLKSIZE contain the information necessary to complete the data control block. The block size, which in this example is 204 x 1024 = 208,896 bytes, must be divisible by the logical record length, and each program that reads or writes this data set must be capable of handling block sizes this large.

BLKSZLIM parameter

Parameter Type

Keyword, optional

Purpose

Use the BLKSZLIM parameter to specify an upper limit on a data set’s block size if BLKSIZE is omitted from all sources and the system determines the block size for the data set. If a BLKSIZE value is available from any source (such as the DD statement, data set label, or the program), then the block size limit has no effect. The BLKSZLIM parameter is useful mainly when writing new magnetic tape data sets with programs that can handle blocks longer than 32,760 bytes. Currently the maximum block size supported on any tape is 256 KB. You can safely code a larger value for BLKSZLIM. The BLKSZLIM value does not have to be a multiple of the LRECL value.

1.Syntax

BLKSZLIM= {value}
          {valueK}
          {valueM}
          {valueG}

2.Subparameter Definition

value
Specifies in bytes an upper limit on a data sets’s block size if BLKSIZE is omitted from all sources and the system determines the block size for the data set. The maximum value is 2,147,483,648 bytes (two gigabytes). The minimum value is 32K (32,768 bytes).

valueK
Specifies the block size limit in kilobytes (units of 1024). The maximum value is 2,097,152K (two gigabytes). The minimum value is 32K.

valueM
Specifies the block size limit in megabytes (units of 1024K). The maximum value is 2048M (two gigabytes). The minimum value is 1M.

valueG
Specifies the block size limit in gigabytes (units of 1024M). The maximum allowable value is 2G (two gigabytes). The minimum value is 1G.

3.Defaults
If you omit BLKSZLIM, the system determines the block size from one of the following sources, starting with the first:

  1. Data class
  2. DEVSUPxx value
  3. 32,768

4.Relationship to Other Parameters
The system ignores BLKSZLIM when you specify BLKSIZE.

5.Example of the BLKSZLIM Parameter

//DD1BB  DD  DSNAME=EVER,DISP=(NEW,KEEP),UNIT=3390,
//           RECFM=FB,LRECL=326,BLKSZLIM=32760,
//           SPACE=(23472,(200,40))

DD statement DD1B defines a new data set named EVER on a 3390 DASD. The DD keywords RECFM and LRECL contain the information necessary to complete the data control block. BLKSZLIM places an upper limit on the block size to be determined by the system.

//DD2B   DD  DSNAME=NEVER,DISP=(NEW,KEEP),UNIT=3590,
//           RECFM=FB,LRECL=80,BLKSZLIM=40K

DD statement DD2B defines a new data set named NEVER on a 3590 TAPE device. The DD keywords RECFM and LRECL contain the information necessary to complete the data control block. BLKSZLIM places an upper limit on the block size to be determined by the system.

BURST parameter

Parameter Type

Keyword, optional

Purpose

Use the BURST parameter to specify that the output for this sysout data set printed on a continuous-forms AFP printer is to go to:

  • The burster-trimmer-stacker, to be burst into separate sheets.
  • The continuous forms stacker, to be left in continuous fanfold.

If the specified stacker is different from the last stacker used, or if a stacker was not previously requested, JES issues a message to the operator to thread the paper into the required stacker.

Note: BURST applies only for an output data set printed on an AFP printer equipped with a burster-trimmer-stacker.

1.Syntax

BURST= {YES}
       {Y }
       {NO }
       {N }

2.Subparameter Definition

YES
Requests that the printed output is to be burst into separate sheets. This subparameter can also be coded as Y.

NO
Requests that the printed output is to be in a continuous fanfold. This subparameter can also be coded as N.

3.Defaults
If you do not code a BURST parameter, but you code a DD SYSOUT parameter and the sysout data set is printed on an AFP printer that has a burster-trimmer-stacker, JES uses an installation default specified at initialization. If you do not code a BURST parameter or a DD SYSOUT parameter, the default is NO.

4.Overrides
A BURST parameter on a sysout DD statement overrides an OUTPUT JCL BURST parameter.

5.Relationship to Other Parameters
Do not code the following parameters with the BURST parameter.

*        DISP       PROTECT
AMP      DSID       QNAME
DATA     DYNAM      VOLUME
DDNAME   LABEL

6.Relationship to Other Control Statements
The burster-trimmer-stacker can also be requested using the following:

  • The BURST parameter on the OUTPUT JCL statement.
  • The STACKER parameter on the JES3 //*FORMAT PR statement.
  • The BURST parameter on the JES2 /*OUTPUT statement.

7.Example of the BURST Parameter

//RECORD DD SYSOUT=A,BURST=Y

In this example, the DD statement requests that JES send the output to the burster-trimmer-stacker of the AFP printer. The stacker separates the printed output into separate sheets instead of stacking it in a continuous fanfold.


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