VSAM Introduction

VSAM Tutorial Topics Index VSAM Dataset Types

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What is VSAM?


VSAM Stands for Virtual Storage Access Method.

VSAM is a data access method which is introduced in 1970’s.

VSAM is an access method in the mainframe operating system.

VSAM enables access to data on disk, tape or other external devices.

VSAM is the first access method that efficiently uses the storage and modifies only the data that exists on direct access storage device.

VSAM can store and access the data from the files in the form of records.

VSAM supports fixed and variable length records.

VSAM contains a data component and index component.

VSAM data component contains the actual data stored in VSAM.

VSAM index component contains the pointers to data stored in VSAM.

VSAM was introduced in 1979 with integrated catalog facility (ICF) to replace the old VSAM catalog of the previous versions.

The latest version of VSAM released in 1991 called VSAM 3.3 which contains enhancements like variable length support for RRDS and added DFSMS facilities.


Advantages:


  • Data retrieval will be very fast when compared to other access methods hence it will use organized index.
  • VSAM datasets can be shared across the systems and regions.
  • The index used in VSAM is small which will use less memory to store hence it uses a key compression algorithm.
  • Insertion of records is easy when compared to the other methods.
  • Records can be physically deleted and the spaces used by them can be used for storing other records without reorganization which helps for faster retrieving.
  • VSAM is independent of storage device types.
  • Datasets can be physically distributed over various volumes based on key ranges.
  • Information of any VSAM dataset need not be detailed in JCL and only providing the small information is sufficient hence the about the VSAM Storing centrally.

Disadvantages:


  • VSAM only provides the security at the dataset level and it any other security level requires then it should be handled by the user.
  • VSAM has very limited support for data sharing across regions.

VSAM Tutorial Topics Index VSAM Dataset Types

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