Determine if you want Bus-level protection based on the following:
- Bus failures are rare in comparison to other disk-related hardware failures.
- The system can continue to operate after a bus failure.
- The system cannot operate if bus 1 fails.
- If a bus fails, disk I/O operations may continue, but other hardware is lost (such as work stations, printers and communication lines) making the system unusable.
- Concurrent maintenance is not possible for bus failures.
To achieve bus-level protection, all disk units that are attached to a bus must have a mirrored unit attached to a different bus. Bus-level protection is not possible for unit 1.
This figure shows the elements of bus-level protection: one expansion unit that contains two buses attached to separate IOPs, IOAs, and disk units, respectively. The two storage units make a mirrored pair.