Hello,
Likely the two controllers are not in sync. Unfortunately without access to the system it is hard to tell what is occurring. I woudl suggest a period of downtime to try the following.
Shutdown both controllers. Controller B may not accept the command but Controller A will and will be shutdown correctly.
CLI# shutdown both
Once the controllers have shutdown remove power. Unseat controller A and all the hard drives. You don't have to remove them put disengage them from the backplane. If there are additional drive enclosures, label the cables and unplug the connecting SAS cables. You should be left witth just the raid head enclosure and controller B. Reconnect the power and bring controller B back online.
Once the controller has powered up fully, check if there is any unwritten cache.
# show unwritable-cache
Clearing unwritable cache can cause data loss, so be careful here on next steps. If there is cache you need to check and confirm whether that cache has already been written to a volume or not. Once you confirm the cache status as 0 set the controller to single controller mode as you did previously.
CLI # set advanced-settings single-controller enabled
You will then be able to upgrade controller B. Once the controller is upgraded power down and reconnect everything you previously disconnected. Powering back on will resync the controllers.
If you power down and still cannot access controller B it will likely need a factory reset which is not something a customer can perform. You will need to log a support ticket for a new controller.
Good Luck!
Cheers,
Shawn
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