I have two Dell PowerEdge R620 Servers running Windows 2012. Added three new drives to the first. The plan was to create a new mirror drive and have the third disk as the hot spare. Server enclosure did not see them. This was a hot add while the server was powered on.
Attempted the same procedure on the second server and the drives were recognized and the new RAID was created without issue. The RAID card is a PERC H710 is the same on both servers. Same drivers and firmware between them as well.
I can reboot, but will have to wait till the weekend. But this is bothering me as the server is supposed to be able to add drives while running. And the second server confirms this is indeed possible.