You're not going to 'lose' any of your data. I assume you built the server with at least two HDDs attached and the HDD capacity is the same as the drive with your media. Just copy the files across ( because you will want a copy outside the beta) and you are ready to go. I suppose when the OS goes RTM people will start slinging any old drives floating around into their brand new box and this forum will fill up with tales of woe regarding failed HDDs but personally I would only put fresh drives into the server.