Determine the amount of control interval free space based on the percentage of record additions expected, and their distribution:

No additions. If no records will be added and if record sizes will not be changed, there is no need for free space.

Few additions. If few records will be added to the data set, consider a free space specification of (0 0). When records are added, new control areas are created to provide room for additional insertions.

If the few records to be added are fairly evenly distributed, control interval free space should be equal to the percentage of records to be added. (FSPC (nn 0), where nn equals the percentage of records to be added.)

Evenly distributed additions. If new records will be evenly distributed throughout the data set, control area free space should equal the percentage of records to be added to the data set after the data set is loaded. (FSPC (0 nn), where nn equals the percentage of records to be added.)

Unevenly distributed additions. If new records will be unevenly distributed throughout the data set, specify a small amount of free space. Additional splits, after the first, in that part of the data set with the most growth will produce control intervals with only a small amount of unneeded free space.

Mass insertion. If you are inserting a group of sequential records, take full advantage of mass insertion by using the ALTER command to change free space to (0 0) after the data set is loaded. For more information about mass insertion see Inserting and Adding Records.

Additions to a specific part of the data set. If new records will be added to only a specific part of the data set, load those parts where additions will not occur with a free space of (0 0). Then, alter the specification to (n n) and load those parts of the data set that will receive additions. The example in Altering the Free Space Specification When Loading a Data Set demonstrates this.