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In transparent failover, units D00 through D99 are accessed through port 1
of both controllers. Units D100 through D199 are accessed through port 2 of
both HSG80 controllers (with the limit of a total of 128 storage units).
You cannot achieve a no-single-point-of-failure (NSPOF) configuration using
transparent failover. The host cannot initiate failover, and if you lose a host
bus adapter, switch, or a cable, you lose the units behind at least one port.
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 failover 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.
Using Fibre Channel Storage 6–11