|Someone didn't know about drive fault tolerance when building this server. Oh well.|
Did you configure the new drive to NOT do termination? This is assuming you are using an active terminator on the end of the scsi cable. If you are using the 4th drive for termination you need to set it to none and this 5th drive to do termination.
Much better to use an active terminator at the end of the cable.
You have to initialize the drive in the scsi bios once you get termination solved.
Then you go into disk management to see the drive, partition, format it and assign it a drive letter.