Compaq TruCluster Server AA-RHGWB-TE, Manual

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You can, however, add the hardware for a second bus (another KGPSA,
switch, and RA8000/ESA12000 with associated cabling) and use LSM to
mirror across the buses. However, because you cannot use LSM to mirror
the cluster root (
/
) file system, member boot partitions, the quorum disk,
or swap partitions you cannot obtain an NSPOF transparent failover
configuration, even though you have increased availability.
6.3.2 Fibre Channel Cluster Configurations for Multiple-Bus Failover
Mode
With multiple-bus failover:
• The host controls the fail over by accessing units over a different path or
causing the access to the unit to be through the other HSG80 controller
(one controller does not fail over to the other controller of its own accord).
• Each cluster member system has two or more KGPSA host bus adapters
(multiple paths to the storage units).
• Normally, all available units (D0 through D199, with a limit of 128
storage units) are available at all host ports. Only one HSG80 controller
will be actively doing I/O for any particular storage unit.
However, both controllers can be forced active by preferring units to
one controller or the other (
SET unit PREFERRED_PATH=THIS
). By
balancing the preferred units, you can obtain the best I/O performance
using two controllers.
_____________________ Note _____________________
If you have preferred units, and the HSG80 controllers restart
because of an error condition or power failure, and one
controller restarts before the other controller, the HSG80
controller restarting first will take all the units, whether
they are preferred or not. When the other HSG80 controller
starts, it will not have access to the preferred units, and will
be inactive.
Therefore, you want to ensure that both HSG80 controllers
start at the same time under all circumstances to ensure
that the preferred units are seen by the controller they are
preferred to.
Figure 6–5, Figure 6–6, and Figure 6–7 show three different multiple-bus
NSPOF cluster configurations. The only difference is the fibre-optic cable
connection path between the switch and the HSG80 controller ports.
6–10 Using Fibre Channel Storage