Ex1,   In regards to your questions regarding updating the controller on the ME4, it should be updated with PFU selected, and the system will remain up while updating as it actually only updates one controller at a time.   It would be the HDD updates that are different and require a full outage.    Let me know if this helps.    
Hi, I am running a cluster with four hosts and a ME4024 dual controller storage. I want to update the firmware without any downtime on the hosts. So first I will check the health status via ssh: check firmware-upgrade-health Upgrade Health If the check is fine I will upload the firmware file via the gui. I have checked the administator guide and the best practice guide but there is no clear statement. How can I be sure, that the firmware update is only running successfull on one controller and after that on the partner controller? I am afraid that it will run the update on both controllers at the same time. Do I need to check or uncheck the PFU box? Thanks!
ME4 4024 Best practice - Firmware update