You need to disassociate the "non-RAID" disk from the controller and convert it to a RAID disk so it can be used in an array.  In CTRL-R, you Initialize the disk, then convert to RAID disk.  Then assign it as a hot-spare to begin the rebuild. [URL] In OMSA, you probably just need to delete the non-RAID VD, then assign it as a hot-spare (no initialization).  If it doesn't allow you to do that, then you will need to do that in the BIOS utility for the S110 (the OMSA documentation mentions this feature for the H310, but not the S110, so it may not support it from OMSA).
PE T320 Windows Server 2008R2 BIOS Up to Date I have a RAID 5 array consisting of (3) 500 GB disks and Perc S110 Controller.  All are Hot-Swap SATA Drives.  I've purchased a 4th SATA Drive, same capacity and speed.  Powered down, inserted drive and restarted. I went straight to OMSA (7.2) and, although first drive is visible, shows as Normal and Non-RAID, the only drop down choices are Blink and Unblink. So I rebooted and entered BIOS Configuration.  Again, new drive appears but Manage Hot Spare(s) option is grayed out and not selectable. I'm not sure what I'm doing wrong and any help would be appreciated.  As a side note, activity light on new disk is blinking consistently. Thanks in advance.  
Assistance Adding Hot Spare