Defining the GDG model data set

You must provide a data control block (DCB) to be used when GDG entries are created. You can provide it when you define the generation data group (GDG) model data set. To define the GDG model data set, use the z/OS® program IEFBR14.

Sample JCL to define a GDG model data set using IEFBR14

The following example provides sample JCL to define a GDG model data set, including the DCB information.

//* STEP1 - Define the GDG Base
//STEP2    EXEC PGM=IEFBR14
//BLDDSCB  DD DSN=BPEEXTRC.GDG01,
//            DISP=(NEW,KEEP),
//            UNIT=SYSDA,
//            VOL=SER=PAGE01,
//            SPACE=(TRK,(0)),
//            DCB=(DSORG=PS,LRECL=32756,RECFM=VB,BLKSIZE=32760)

You can also pass the DCB information using the DSN parameter on the EXTTRACE statement. However, you cannot override the data set attributes.

You must define the data set with RECFM=VB, and an LRECL that is 4 bytes less than the BLKSIZE. The minimum supported BLKSIZE is 8340.

Recommendation: Use a large block size (such as the maximum of 32 760). Using a large BLKSIZE ensures that multiple records are written per block. In addition, you would not have to change your BPE external trace definitions if the minimum supported block size is ever increased.

For more information on IEFBR14, see z/OS MVS JCL Reference.