Technical data

• Normally, all available units (D0 through D199) are available at all
host ports. Only one HSG80 controller will be actively doing I/O for
any particular storage unit.
However, both controllers can be forced active by preferring units to
one controller or the other (
SET unit PREFERRED_PATH=THIS). By
balancing the preferred units, you can obtain the best I/O performance
using two controllers.
_____________________ Note _____________________
If you have preferred units, and the HSG80 controllers restart
because of an error condition or power failure, and one
controller restarts before the other controller, the HSG80
controller restarting first will take all the units, whether
they are preferred or not. When the other HSG80 controller
starts, it will not have access to the preferred units, and will
be inactive.
Therefore, you want to ensure that both HSG80 controllers
start at the same time under all circumstances so that the
controller sees its own preferred units.
Figure 6–6 and Figure 6–7 show two different recommended multiple-bus
NSPOF cluster configurations. The only difference is the fiber-optic cable
connection path between the switch and the HSG80 controller ports.
There is no difference in performance between these two configurations. It
may be easier to cable the configuration shown in Figure 6–6 because the
cables from one switch (or switch zone) both go to the ports on the same side
of both controllers (for example, port 1 of both controllers).
Using Fibre Channel Storage 6–11