Controller states
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You can place a controller into three different states: online, offline, and service mode.
Online state
The online state is the normal operating state of the controller. It means that the controller is operating normally and is available for I/O operations.
When you place a controller online, its status is set to optimal.
Offline state
The offline state is typically used to prepare a controller for replacement when there are two controllers in the storage array. A controller can enter the offline state in two ways: you can issue an explicit command or the controller can fail. A controller can exit the offline state only by issuing another explicit command or by replacing the failed controller. You can place a controller offline only if there are two controllers in the storage array.
When a controller is in the offline state, the following conditions are true:
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The controller is not available for I/O.
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You cannot manage the storage array through that controller.
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Any volumes currently owned by that controller are moved to the other controller.
Service mode
Service Mode is typically used only by technical support to move all storage array volumes to one controller so that the other controller can be diagnosed. A controller must be manually placed in service mode and must be manually placed back online after the service operation is completed.
When a controller is in service mode, the following conditions are true:
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The controller is not available for I/O.
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Technical support can access the controller through the serial port or network connection to analyze potential problems.
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Any volumes currently owned by that controller are moved to the other controller.
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Cache mirroring is disabled and all volumes are changed to write through cache mode.