You are getting a hardware alert for a degraded disk - 'Detect Imminent Failure' as shown below during server reboot. This alarm persists even with updated iLO and BIOS firmware. You would like to know how to get rid of this warning message.
The degraded disk needs to be replaced in this case.
Note: if you have any unassigned disks on the server, you can use one of them to replace the degraded disk. There is no need to shut down the server to do that, just eject the drives and insert in the position where the faulty one is, then it will start re-silvering automatically.
The warning message should disappear after replacing the disk.