We have a PDC running Server 2008 and backup DC running Server 2003. Last week the PDC had a hard drive failure and was down. After about 1 day the users could not get authenticated and DNS information was not available to clients so Shares and mapped drives started to disappear. Of course without DHCP new clients such as mobile laptops couldnt even get IP addresses. Should the backup DC taken over automatically or did it need to be promoted, what about DHCP? Both servers are back up and running now. I want to make sure if this happens again we can continue to work until the PDC is repaired.