Types of Catalog-VSAM

Types of Catalog based on Function

a.      Master Catalog

Every system that uses VSAM has one, and only one, master catalog.  The master catalog contains entries about system datasets and VSAM structures used to manage the operation of VSAM.  It is possible for any dataset (VSAM or non-VSAM) to be cataloged in the master catalog, but that is rarely allowed in well managed systems. 

b.     User Catalogs

A user catalog is a catalog created to contain entries about application specific datasets.  The information defining a user catalog is stored into a catalog entry in the master catalog. 
There is no structural difference between a MCAT and a UCAT. What makes a MCAT different is how it is used and what datasets are cataloged in it.

ICF Catalog
An ICF has 2 components:

a.      BCS (Basic Catalog Structure)
BCS can be considered as the Catalog. In ICF whenever an user/master catalog is created using IDCMAS a BCS is created. The BCS is a VSAM KSDS and its primary function is to point to the volumes on which a dataset is located. It uses the dataset name as a key to store and retrieve dataset information.

b.     VVDS (VSAM Volume Dataset)
VVDS is a VSAM ESDS file that contains the information required to process VSAM datasets. It contains additional information about VSAM and SMS mamaged non-VSAM datasets residing on the colume where the VVDS is located.
The VVDS is composed of minimum 2 records:
a.       VSAM Volume Control Record(VVCR) – Contains info for management of DASD space
b.       VVDS self describing volume record – contains info that describes the VVDS
c.       The remaining logical records in the VVDS are VVR(VSAM Volume Records) for VSAM datasets and NVR(Non-VSAM Volume Records) for SMS-managed non-VSAM datasets. 


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