To determine the number of cylinders required for an indexed sequential
data set, you must consider the number of blocks that will fit on
a cylinder, the number of blocks that will be processed, and the amount
of space required for indexes and overflow areas. When you make the
computations, consider how much additional space is required for device
overhead. The IBM documents for storage devices contain device-specific
information on device capacities and overhead formulas. Refer to the
document written for your device. In the formulas that follow, the
length of the last (or only) block must include device overhead.
Blocks = Track capacity / Length of blocks
Use modulo-32 arithmetic when calculating key length and data length
terms in your equations. Compute these terms first, then round up
to the nearest increment of 32 bytes before completing the equation.
The following eight steps summarize calculation of space requirements
for an indexed sequential data set.