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6.7.1 Overview
The change in failover modes cannot be accomplished with a simple SET
MULTIBUS COPY=THIS HSG80 CLI command because:
• Unit offsets are not changed by the HSG80 SET MULTIBUS_FAILOVER
COPY=THIS command.
Each path between a Fibre Channel host bus adapter in a host computer
and an active host port on an HSG80 controller is a connection. During
Fibre Channel initialization, when a controller becomes aware of a
connection to a host bus adapter through a switch, it adds the connection
to its table of known connections. The unit offset for the connection
depends on the failover mode in effect at the time the connection is
discovered. In transparent failover mode, host connections to port 1
default to an offset of 0; host connections on port 2 default to an offset
of 100. Host connections on port 1 can see units 0 through 99; host
connections on port 2 can see units 100 through 199.
In multiple-bus failover mode, host connections on either port 1 or 2
can see units 0 through 199. In multiple-bus failover mode, the default
offset for both ports is 0.
If you change the failover mode from transparent failover to multiple-bus
failover, the offsets in the table of known connections remain the same as
if they were for transparent failover mode; the offset on port 2 remains
100. With an offset of 100 on port 2, a host cannot see units 0 through 99
on port 2. This reduces the availability. Also, if you have only a single
HSG80 controller and lose the connection to port 1, you lose access to
units 0 through 99.
Therefore, if you want to change from transparent failover to
multiple-bus failover mode, you must change the offset in the table of
known connections for each connection that has a nonzero offset.
_____________________ Note _____________________
It would do no good to disconnect and then reconnect the
cables, because once a connection is added to the table it
remains in the table until you delete the connection.
• The system can access a storage device through only one HSG80 port.
The system’s view of the storage device is not changed when the HSG80
is placed in multiple-bus failover mode.
In transparent failover mode, the system accesses storage units D0
through D99 through port 1 and units D100 through D199 through port
2. In multiple-bus failover mode, you want the system to be able to
access all units through all four ports.
6–58 Using Fibre Channel Storage