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2–30 Configuring an HSZ80 Array Controller
■ For better subsystem performance, balance your assignment of target ID numbers
across your dual-redundant pair of controllers. For example, if you are presenting
four targets to the host, prefer two to one controller and two to the other
controller.
■ Balance your assignment of devices. For example, in an 18-device subsystem,
place 3 devices on each of the 6 ports, rather than placing 6 devices on each of 3
ports.
■ The controller to which you copy configuration information restarts after you
enter the SET FAILOVER command.
Using Multiple-Bus Failover Mode
Multiple-bus (or host-assisted) failover is a dual-redundant controller configuration in
which each controller has its own connection to the host. Thus, if one of the host
connections to a controller fails, the host can cause units that became inaccessible to
failover to the remaining viable connection. Because both controllers service the same
storage units, either controller can continue to service all of the units if the other
controller fails.
Keep the following points in mind when configuring controllers for multiple-bus
failover:
■ The host distributes the I/O load between the controllers.
■ The host must have two SCSI adapters as well as operating-system software to
support the multiple-bus failover, dual-redundant controller configuration.
■ SCSI target ID number and LUN configurations on each controller must be
identical.
■ Mount both controllers in the same BA370 rack-mountable enclosure and follow
the steps in “Configuring an HSZ80 Array Controller,” page 2–3.
■ Partitioning is not supported.