Compaq StorageWorks HSG60 ACS Solution Software V8.6 for Compaq Tru64 UNIX Installation and Configuration Guide

Planning a Subsystem 1–7
All hosts must have operating system software that supports multiple-bus failover
mode.With this software, the host sees the same units visible through two (or more) paths.
When one path fails, the host can issue commands to move the units from one path to
another. A typical multiple-bus failover configuration is shown in Figure 1–5.
In multiple-bus failover mode, you can specify which units are normally serviced by a
specific controller of a controller pair. This process is called preferring or preferment.
Units can be preferred to one controller or the other by the PREFERRED_PATH switch of
the ADD (or SET) UNIT command. For example, use the following command to prefer
unit D101 to “this controller”:
SET D101 PREFERRED_PATH=THIS_CONTROLLER
NOTE: This is an initial preference, which can be overridden by the hosts.
Keep the following points in mind when configuring controllers for multiple-bus failover:
■ Multiple-bus failover can compensate for a failure in any of the following:
❏ Controller
❏ Switch or hub
❏ Fibre Channel link
❏ Host Fibre Channel adapter
■ A host can redistribute the I/O load between the controllers.
■ All hosts must have operating system software that supports multiple-bus failover
mode.