Excerpt of attached PDF:
NOTE: It is VERY IMPORTANT that you replace a failed redundant controller WITH
POWER ON! Since, at power on, the controllers compare their internal serial numbers to
determine which will become Primary (HIGHER S/N = Primary), the replacement
controller needs to get its’ configuration (and/or firmware) from the surviving controller.
IF the replacement controller has a higher S/N AND it was installed with power-off, then
the GOOD controller (i.e. survivor) will download the configuration & firmware of the
replacement controller and this is most likely to be default values! This means that you
could lose all of you LUN mappings, Partition sizes, WWN Filter Masks, etc!
Download the full document below.