HP StorageWorks HSG80 ACS Solution Software V8.8 for Novell NetWare Installation and Configuration Guide (AA-RV1MA-TE, March 2005)

Planning a Subsystem
31HSG80 ACS Solution Software V8.8 for Novell NetWare 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 or, in multiple-bus mode only, due to a failure of
the link between host and controller or host-bus adapter. Failover keeps the
storage array available to the hosts by allowing the surviving controller to take
over total control of the subsystem.
There are two failover modes:
■ Transparent, which is handled by the surviving controller and is invisible
(transparent) to the hosts.
■ Multiple-bus, which is handled by the surviving controller and which is
handled by the hosts through either additional software or as a feature of the
operating system.
Either mode of failover can work with loop or fabric topology.
Note: Multiple-bus failover mode is only supported when Secure Path is used. Refer to
the Secure Path documentation for more information on using multiple-bus mode.
Transparent Failover Mode
Transparent failover mode has the following characteristics:
■ Hosts do not know failover has taken place.
■ Units are divided between host ports 1 and 2.
A unit or storageset is a physical or virtual device of the subsystem. It is typically
assigned a logical unit number (LUN) and is managed by the HSG80 controller
and presented to a server through the Fibre Channel bus and the server’s host bus
adapter. Disks that are set up as independent disks (JBODs) or RAIDsets are
referred to as storagesets.
In transparent failover mode, host port 1 of controller A and host port 1 of
controller B must be on the same Fibre Channel link. Host port 2 of controller A
and host port 2 of controller B must also be on the same Fibre Channel link.
Depending on operating system restrictions and requirements, the port 1 link and
the port 2 link can be separate links, or they can be the same link.