First, calculate the amount of space needed for the primary allocation. If the data set is larger than one cylinder, calculate and specify the number of cylinders needed for data in a newly defined data set for the primary allocation. Make the secondary allocation equal to or greater than one cylinder, but less than the primary allocation. Calculating Space for the Data Component of a KSDS demonstrates how to calculate the size of a data set.
See Using Index Options for information about index options.