Control area size has significant performance implications. One-cylinder control areas have the following advantages:

• There is a smaller probability of control area splits.
• The index is more consolidated. One index record addresses all the control intervals in a control area. If the control area is large, fewer index records and index levels are required. For sequential access, a large control area decreases the number of reads of index records.
• There are fewer sequence set records. The sequence set record for a control area is always read for you. Fewer records means less time spent reading them.
• If the sequence set of the index is imbedded on the first track of the control area, it is replicated to reduce the rotational delay inherent when reading from the device.
• If you have allocated enough buffers, a large control area lets you read more buffers into storage at one time. A large control area is useful if you are accessing records sequentially.