In access method control block (ACB)

The system obtains access method control block information for VSAM data sets from the following sources, in override order:

The AMP subparameters on the DD statement.

   //ddname  DD  AMP=(subparameter),...
   //ddname  DD  AMP=('subparameter,subparameter,...'),...

With SMS, the DD statement parameters KEYLEN, KEYOFF, LRECL, and RECORG.
The ACB, EXLST, or GENCB macro instructions in assembler language programs.
The catalog entry for the data set.

Therefore, the system ignores a value in a program macro instruction if the DD AMP parameter supplies the value. The system ignores a value in the data set catalog entry if the access method control block already contains the value from a DD AMP subparameter or a macro instruction in the program.

Note: The override order for ACB values is different from the override order for DCB values.

Examples

//DD4  DD  DSNAME=ANYVSAM1,AMP=('BUFND=4,BUFNI=4,STRNO=2'),
//     DISP=(NEW,CATLG,DELETE),UNIT=3380,VOLUME=556677,
//     SPACE=(TRK,(200,50))