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Each array has one or two control modules installed. Only one functioning control module is required for operation.
Caution: Only install control modules of the same type in an array. Do not mix control module types in an array.
When a dual control module array starts, one control module is designated as active (responsible for serving I/O to the member), while the other control module is secondary (mirrors cache data from the active control module). Upon startup, either control module can be designated active or secondary, regardless of its previous status. The active control module is designated by the green LED labeled ACT.
Under normal operation, the status of a control module (active or secondary) will not change, unless the member is restarted. However, if the active control module encounters a failure, the secondary control module will take over and serve I/O. This is called control module failover.
Control module management topics include the following: