If you use a V5R2 input/output adapter (IOA) and OS/400® V5R2 or later, you can now choose how you want your parity sets to be optimized. When you select to optimize a parity set, the I/O adapter will choose disk units for parity sets according to the optimization value you have chosen. Depending on your configuration, different parity set optimizations might generate the same parity sets. You have several options for parity set optimization:
A parity set optimized for availability offers a greater level of protection because it allows a parity set to remain functional in the event of a I/O bus failure. The availability optimization value ensures that a parity set is formed from at least three disk units of equal capacity each attached to a separate bus on the input/output adapter (IOA). For example, if an I/O adapter had 15 disk units and was optimized for availability, the result might be five parity sets with three disk units each attached to separate I/O buses on the adapter. OS/400 V5R3 is required to optimize for availability.
A parity set optimized for capacity stores the most data possible. The I/O adapter may generate fewer parity sets with more disk units in each parity set. For example, if an I/O adapter has 15 disk units and is optimized for capacity, the result might be one parity set containing 15 disk units.
A balanced parity set compromises between the ability to store large amounts of data and also provide fast access to data. For example, if an I/O adapter has 15 disk units and you choose balanced parity optimization, the result might be two parity sets, one with nine disk units and one with six disk units.
Parity sets optimized for performance provide the fastest data access. The I/O adapter may generate more parity sets with fewer numbers of disk units. For example, if an I/O adapter had 15 disk units and is optimized for performance, the result might be three parity sets with five disk units each.