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3.7.1.2 Preparing a Dual-Redundant HSZ70 or HSZ80 for a Shared SCSI Bus Using
Multiple-Bus Failover
Multiple-bus failover is a dual-redundant controller configuration in which
each host has two paths (two shared SCSI buses) to the array controller
subsystem. The host(s) have the capability to move LUNs from one controller
(shared SCSI bus) to the other. If one host adapter or SCSI bus fails, the
host(s) can move all storage to the other path. Because both controllers
can service all of the units, either controller can continue to service all of
the units if the other controller fails. Therefore, multiple-bus failover can
compensate for a failed host bus adapter, SCSI bus, or RAID array controller,
and can, if the rest of the cluster has necessary hardware, provide a NSPOF
configuration.
______________________ Note _______________________
Each host (cluster member system) requires at least two
KZPBA-CB host bus adapters.
Although both the HSZ70 and HSZ80 have multiple-bus failover, it operates
differently:
• HSZ70: Only one controller (or shared SCSI bus) is active for the
units that are preferred (assigned) to it. If all units are preferred to
one controller, then all units are accessed through one controller. If a
controller detects a problem, all of its units are failed over to the other
controller. If the host detects a problem with the host bus adapter or SCSI
bus, the host initiates the failover to the other controller (and SCSI bus).
• HSZ80: Both HSZ80 controllers can be active at the same time. If the
host detects a problem with a host bus adapter or SCSI bus, the host
initiates the failover to the other controller. If a controller detects a
problem, all of its units are failed over to the other controller.
Also, the HSZ80 has two ports on each controller. If multiple-bus failover
mode is enabled, the targets assigned to any one port are visible to
all ports unless access to a unit is restricted to a particular port (on a
unit-by-unit basis).
To cable an HSZ70 or HSZ80 for multiple-bus failover in a TruCluster Server
configuration using DS-DWZZH-03 or DS-DWZZH-05 UltraSCSI hubs (you
need two hubs), see Figure 3–7 (HSZ70) and Figure 3–8 (HSZ80) and follow
these steps:
1. Install an H8863-AA VHDCI terminator on each of two H8861-AA
VHDCI trilink connectors.
3–22 Shared SCSI Bus Requirements and Configurations Using UltraSCSI Hardware