1. Is the light is amber and blinking, just try to restart the controller in: tools–restart or shutdown controller, then chose in operation: restart, controller type: storage, controller: (A or B) depend of the controller that have failed, and then press restart, this step is just to see if the controller failed because had some electrical problem like static.
   

2. If the previous method doesn’t work and the controller do not come up, maybe is time to replace it, just click in the icon of the enclosure and choose rear graphic in the right panel, below to the enclosure image there are information about the hardware to replace, just click in the failed controller and get the part number, buy it.
Once you have the new controller do the next steps:

3. Go again to the menu: tools–restart or shutdown controller, again choose operation: shutdown, controller type: storage, controller: (A or B) depend of the controller that have failed, and the press shutdown. If the controller doesn’t want to go down, maybe is because is already down, is time to remove the controller.

4. Disconnect the fiber cable and the SAS cable if exist.

5. Remove the controller, first take out the screw in both sides of the controller, after that just move down, rotating back and down, the lever, something this need a lot of energy, double check the screw, and pull out the controller, just wait 30 second before to insert the new one.

6. Before to insert the new one, go to the management web interface again, look in configuration–advanced settings–firmware and check the option Partner firmware update, and press apply, hp recommend it in systems with 2 controllers, specially configured with failover, to keep the controller working in the same way, using the same firmware.

6. Insert the new one, but just push the controller, some light are going to come up, but don’t put the lever yet, wait 10 seconds, now put the lever back, remember is rotating it up and pushing it forward, after that put the screw again.

7. The system is going to update the firmware, need the same firmware in both controller, is going to update with the last firmware in the controller, if both controller have different firmware, is going to update with the last of both, this procedure is going to take like 10 to 20 minutes, just wait. Put back the cables, fiber, network and SAS cables.
(if the controller never come up, try to restart it in tools–restart and shutdown controller).

8. If the OS is using multipath, for instance linux with multipath, just see if the multipath service is running, if the service is running, after the replacement of the controller, when all the procedure is finished, the multipath is going to recognize the new path and put it back in enable mode, is the multipath show the partition still as failed, then is very possible that the service is not running.
Check the path status with ” multipath -l ” command, and check if the service is running with systemctl list-units –type service –all, and the status of the service with systemctl status multipathd, old systems with the command ps aux | grep multipath.