HP StorageWorks HSG80 ACS Solution Software V8.8 for OpenVMS Installation and Configuration Guide (AA-RV1PA-TE, March 2005)

Planning a Subsystem
29HSG80 ACS Solution Software V8.8 for OpenVMS Installation and Configuration Guide
What is Failover Mode?
Failover is a way to keep the storage array available to the host if one of the
controllers becomes unresponsive. A controller can become unresponsive because
of a controller hardware failure. Failover keeps the storage array available to the
hosts by allowing the surviving controller to take over total control of the
subsystem.
Multiple-Bus Failover Mode
Multiple-bus failover mode has the following characteristics:
■ Host controls the failover process by moving the units from one controller to
another
■ All units (0 through 199) are visible at all host ports
■ Each host has two or more paths to the units
All hosts must have operating system support or additional 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 8.
In multiple-bus failover mode, you can specify which units are normally serviced
by a specific controller of a controller pair. Units can be preferred to one controller
or the other by the PREFERRED_PATH switch of the
ADD UNIT (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