The drac stays up even during a server reboot. You can either power off and unplug the server for a few minutes or you can use racadm from a remote system to do a racadm racreset. [URL]
I had T420 running ESX with 8 drives  (600GB) in RAID-6. I had drive7 fail. I have replaced the drive, and in the RAID utility I have designated it as hot swop. And after the reboot all green lights started blinking, indicating to me that the RAID is being rebuild. It has been two days now. On server all seems to be fine, no orange lights anywhere. However when I log into the iDrac and go to  Storage/Physical Disks, the replaced disc has red circle with white cross next to it, when I see the properties of the Disc, there is nothing obviously wrong with it, state is "online" Also the Storage/Virtual Disks has yellow triangle with exclamation mark next to it, but the state is "online". Advanced properties do not show any obvious issues. When I log into the PERC H710 Adapter BIOS Configuration Utility, PD Mgmt menu shows all discs State as "online" and VD Mgnt menu shows the Virtual Disk to be in "Optimal" state. Why is there the red circle next to mine HD status and the yellow triangel next to the VD status? Thank you Mrcha 
Failed drive on T420?