How to Define IAM Files

Category: JCL and z/OS Utilities

Overview

IAM (Indexed Access Method) files are defined similarly to VSAM KSDS files, with one critical distinction in their definition parameters.

Definition Structure

DEF CL(NAME(DFC2.CP000000.QA.VSO.PDFILE)-
     OWNER($IAM)-
     SPEED -
     IXD-
     CYL(750 450)-
     SHR(2)-
     RECORDSIZE(3900,3900)-
     FREESPACE(15 10)-
     REUSE -
     VOLUMES(* *))-
   DATA(NAME(DFC2.CP000000.QA.VSO.PDFILE.DATA)-
     CISZ(2048)-
     KEYS(7 15)-
     BUFFERSPACE(68608))-
   INDEX(NAME(DFC2.CP000000.QA.VSO.PDFILE.INDEX)-
     CISZ(3584))

Key Distinction

The primary difference between IAM files and standard VSAM KSDS files is the OWNER($IAM) keyword parameter. This designation identifies the file as an IAM-managed dataset and is essential for proper file classification.

Common Parameters

Both IAM and VSAM definitions share standard parameters including space allocation (cylinders), record sizing, free space percentages, data and index component sizing, buffer specifications, and key definitions.