automatically turn on. Before the interconnect-battery unit Service Action Allowed
status LED can turn on, you must use the DS4000 Storage Manager client to
place controller B offline. (Controller A is the controller designated to receive all
I/O activity when the interconnect-battery unit is removed from the DS4800.) By
placing controller B offline, you route all controller and I/O activity through
controller A. This maintains data availability while the interconnect-battery unit is
removed, preventing any problems that would normally arise from the loss of
communication between controllers A and B.
Attention: Before you remove the interconnect-battery unit, you must verify
that controller A is in an optimal state, and the power supply and fan unit CRU
that is connected to controller A (the right power supply) is optimal. Never
remove the interconnect-battery unit when controller A or the power supply and
fan unit CRUs are not in an optimal state.
Multiple component failures
When multiple components in the DS4800 have failed, the behavior of the Service
Action Allowed and Needs Attention LEDs can vary from situation to situation. In
some cases, multiple Service Action Allowed status LEDs light when their
corresponding Needs Attention LEDs are lit. In other cases, none of the Service
Action Allowed status LEDs light when their corresponding Needs Attention LEDs
are lit. This variance exists because the ability to remove a component depends on
the different data availability dependencies of the storage subsystem components.
If replacing any one of the multiple components that have their Needs Attention
LEDs lit will cause the DS4800 Storage Subsystem to shut down, the Service
Action Allowed status LEDs will not light on any of the components that need
attention. For example, if both the right power supply and fan unit (which is linked to
controller A) and controller B need attention, then neither of the Service Action
Allowed status LEDs on these components would light. Removing the controller B
before replacing the failed right power supply and fan unit would cause controller A
to lose power, resulting in a loss of data availability. (This linkage exists because
the power distribution from each power supply and fan unit runs through the
controller physically connected to that power supply and fan unit.)
However, if replacing any one of the multiple components that have their Needs
Attention LEDs lit will not cause the DS4800 Storage Subsystem to shut down, then
the Service Action Allowed status LEDs will light on all of the components that need
attention. For example, if the right power supply and fan unit (which is linked to
controller A) and controller A both need attention, then the Service Action Allowed
status LEDs on both of these components would light, indicating that either
component can be replaced first.
Important: In this situation (in which replacing any one of the multiple components
that have their Needs Attention LEDs lit will not cause the DS4800
Storage Subsystem to shut down), after you remove one failed
component, the Service Action Allowed status LEDs on the remaining
components that need attention might turn off. This change in the
Service Action Allowed status LEDs indicates that removing additional
components now might cause the storage subsystem to shut down.
For example, if both power supply and fan units have failed, the Needs
Attention and the Service Action Allowed status LEDs would be lit for
both components. However, when you remove one power supply and
fan unit from the system, the Service Action Allowed status LED on the
remaining power supply and fan unit turns off, indicating that you now
Chapter 5. Replacing components 143
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