VSAM Cluster

• VSAM datasets are frequently referred to as a Cluster
• A cluster can be thought of as a logical set comprises of two separate physical components:-
  • Data component (which holds actual data)
  • Index component (which holds actual index)
• The cluster concept simplifies the processing of VSAM, making it possible to treat index and data components as a single entity with its own cataloged name. This allows you to process data portion and index portion separately
• All types of VSAM datasets are called clusters, although KSDS only fulfils the concept of the cluster. It means that, the KSDS cluster consists of both, data component and index component. ESDS, RRDS and LDS don’t have index component

Data component

• Data component contains actual data records belonging to that dataset
• Data records in data component are stored as part of unit called as Control Interval (CI) and Control Intervals are stored as part of unit called as Control Area (CA).
• Data Component, Control Interval and Control Area are explained in detail in upcoming article

Index component

• Index components contains the actual index information
• Index component consist of two parts:-
  • Sequence set
  • Index set
• Index component, Sequence set and Index set are explained in detail in upcoming article