Specifications

2–5
Compaq HSG80 Array Controller ACS Version 8.4 Configuration and CLI Reference Guide
Selecting a Failover Mode
When you select a failover mode, your selection determines the way in which your
controller will be configured in the system. This configuration will take into account
how logical units are associated with the controller host ports and how they are
accessed by the host. The logical units are said to fail over to the surviving controller,
essentially granting it access to the logical units.
Failover is the process where a controller loses communication—called the
unresponsive controller—and the surviving controller rapidly takes control of the
system. In transparent failover mode, failover occurs when the controller fails. In
multiple-bus failover mode, failover occurs when the host driver detects it cannot
communicate over a particular path to its LUNs.
Use transparent failover if you want the failover to occur without any intervention
from the host. Use multiple bus failover if the drivers in the host have the capacity to
view multiple instances of a unit. Present one instance to the host and present a
different instance when a path fails. See the documentation for your host operating
system for more details about the drivers.
Once the controller has been fixed or is replaced, then the surviving controller can
transfer back (or fail back) the logical units to it.
Using Transparent Failover Mode
Transparent failover occurs when a controller fails, loss of communication occurs, or
when you press the reset button on one of the controllers.
In transparent failover, two of the four host ports are active and two are standby. This
way, only two host ports at a time allow host access to the logical units. If a controller
failure occurs, then the available standby port automatically becomes active, which
then maintains host access to the logical units. See “Shared Port IDs,” page 2–6 for
more information about the host ports and logical units.
To configure controllers for transparent failover, follow the steps in “Configuring in
Transparent Failover Mode,” page 5–12.