VSAM - Overview

Virtual Storage Access Method (VSAM) is high performance access method and data set organization, which organizes and maintains data via a catalog structure. It utilizes virtual storage concept and can protect datasets at various levels by giving passwords. VSAM can be used in COBOL programs like physical sequential files. VSAM are the logical datasets for storing records. Files can be read sequentially and randomly in VSAM. It is an improved way of storing data which overcomes some of the limitations of conventional file systems like Sequential Files.

Characteristics of VSAM

Following are the characteristics of VSAM −

• VSAM protects data against unauthorized access by using passwords.

• VSAM provides fast access to data sets.

• VSAM has options for optimizing performance.

• VSAM allows data set sharing in both batch and online environment.

• VSAM are more structured and organized in storing data.

• Free space is reused automatically in VSAM files.

Limitations of VSAM

The only limitation of VSAM is that it cannot be stored on TAPE volume. It is always stored on DASD space. It requires a number of cylinders to store the data which is not cost-effective.