After planning for the number and type of storage units needed for each disk pool on the system, and for any spare storage units, add up the total number of storage units of each disk unit type and model. Remember that the number planned is the number of storage units of each disk unit type, not the number of disk units. You and your IBM® marketing representative need to convert the planned number of storage units to disk units before ordering hardware.
The preceding information helps you plan the total number of disk units needed for your system. If you are planning for a new system, this is the number that needs to be ordered. If you are planning for an existing system, subtract the number of each disk type currently on your system from the number that is planned. This is the number of new disk units that should be ordered.