Redundant Server?

I am trying to put together a redundant server that would sycronize all data from the PDC. What I mean is that it would mirror the data files from the Primary Server to the BDC. In the event that the Server went down mid-day, I could promote the BDC to PDC and still have access to that same data from each workstation. I know this is possible somehow. I already have a RAID 1 on the PDC, but I need additional security. Please give me some feedback – thelven@gte.net