Cluster
• It is a collection of physical data sets that makeup one logical data set
• The concept of a cluster is more suited for a KSDS
• A KSDS cluster has two data sets. One holds actual data records and other contains an index component
• Index component permits direct retrieval of data
• With an ESDS and RRDS and an LDS, the cluster name and data set component name both refer to same data set and a cluster consists of only a single physical data set, the data component
Control Interval (CI)
• A Control interval is the amount of data transferred between device and virtual storage
• When a record is read from or written to a data set, VSAM groups individual data records into larger units of storage. These units of storage are called CI
• Size of CI should be minimum 512 bytes and increased by multiples of 512 upto a limit of 8K. beyond that it increments should be 2K upto a maximum of 32K
CI has 4 components
• Data – contains the actual data processed by the program
• CIDF – contains information about the free space within the CI. Its of 4 bytes length
• RDS – contains information about the records within the data space. It is a 3 bye field that is used to define the location and length of a record or a group of records. RDFs immediately precede the CIDF, at he end of control interval
• Freespace – These are the remaining unused space
One comment for “Cluster & CI”
1
I was unaware about the terms Cluster and CI, now I’ve learned that CI is the amount of data transferred between the device and the virtual storage.
August 5th, 2010 at 7:09 pm