Lee Draper,   You are correct in the process that if you have a Predicted Failure drive, that is online, you need to force it offline before removing. Once you force it offline and remove it, the hotspare should start the rebuild then.   Now to answer your last question, all of the steps discussed are to be done with the server powered up and running.    Let me know if this helps.    
Hello all, I have a question that I suspect I know the answer to but I would like to double check. We have a PowerEdge R720 with 7 disks in RAID 5 and one hot spare (PERC H710P Mini). One of the disk is predicted to fail. If I offline the problem disk will the hotswap disk kick in? Can this be done while the server is being actively used? I would have thought so but I cannot find any documentation on this.  Thank you in advance.Lee Draper
Putting a disk into Offline mode