Traditional and Wide Record Formats for Master Files

Products

• Librarian

Issue/Introduction

This document contains corrections to the documentation concerning wide record masterfiles in the System Services Guide. It outlines the differences between Traditional BDAM and VSAM Master files and a Wide Record Master files. It also provides details on record and blocksize limitations for each type of Master file and maximum file sizes.

Environment

Release:
Component: C21E

Resolution

CA Librarian includes the following types of master files:

Traditional Master File

Is a direct-access data set composed of fixed-length blocks. The block length is set when the master file is initialized. Traditional master files, also known as AFO (Advanced File Organization) files, use BDAM or VSAM access methods. The length of a logical record in traditional files is limited to 80-character source or 133-character print-image members. Updates to print-image members are limited to member replacement.

Traditional AFO members are limited to 255 blocks.
When a member is selected for updating, CA Librarian locates the member entry in the index and positions the disk head at the first block of the member.
After the member is updated, CA Librarian records the new entry location in the index and frees the space that the older version occupied.

BDAM files cannot be extended to multiple extents or multiple volumes.
However, VSAM files can span volumes and use secondary extents.
When defining a VSAM data set to use as a master file, primary and secondary space allocations can specified up to 59 volumes.
VSAM allocates up to 118 extents for a maximum data set size of 4.2 GB (4,294,967,296 bytes).
For VSAM files, the logical record length and block size can be as large as 32,760 bytes.

Note: VSAM files cannot be shared between VSE/ESA and VM/ESA.

Wide Record Master File

Is a partitioned data set that must use a PDS or PDS/E format.
When using a PDS formatted file, space is not reused and periodic compressions are required.

Note: Wide record files cannot be shared between VSE/ESA and VM/ESA.

For wide record master files, the logical record length and block size can be as large as 32,760 bytes.
No practical limit exists for the number of blocks per member, and no limitations exist for updating members with logical records longer than 80 characters.
However, ELIPS only allows editing of members with a length of less than 256 characters.
Wide record master files can occupy secondary extents but not multiple volumes.

Wide record master files have an external security interface with the started task LAMSERV.
LAMSERV prevents unauthorized access to master files with standard z/OS and OS/390 utilities and online editors normally available for use with partitioned data sets.

Note: For information about LAMSERV implementation, see the Librarian Installation Guide.