Determine if you want IOP-level protection based on the following:
- To keep your system available when an I/O processor fails.
- To keep your system available when the cable attached to the I/O processor fails.
- To concurrently repair certain types of disk unit failures or cable failures. For these failures, concurrent maintenance needs to reset the IOP. If any disk units that are attached to the IOP do not have IOP-level protection, then concurrent maintenance is not possible.
To achieve IOP-level protection, all disk units that are attached to an I/O processor must have a mirrored unit attached to a different I/O processor. On many systems, IOP-level protection is not possible for the mirrored pair for unit 1.
This figure shows the elements of IOP-level protection: one bus, attached to two IOPs, which are each connected to a separate IOA and a separate disk unit. The two storage units make a mirrored pair. With IOP-level protection, the system can continue to operate if one I/O processor fails. The system becomes unusable only if the bus fails.