Managing Serviceguard 12th Edition, March 2006

Understanding Serviceguard Hardware Configurations
Redundant Disk Storage
Chapter 2 51
Figure 2-8 Root Disks on Different Shared Buses
Note that if both nodes had their primary root disks connected to the
same bus, you would have an unsupported configuration.
You
can put a mirror copy of Node B's root disk on the same SCSI bus as
Node A's primary root disk, because three failures would have to occur
for both systems to boot at the same time, which is an acceptable risk. In
such a scenario, Node B would have to lose its primary root disk and be
rebooted, and Node A would have to be rebooted at the same time Node B
is, for the IODC firmware to run into a problem. This configuration is
shown in Figure 2-9.