We currently have 2 domain controllers running Server 2003 x64. Roles include AD, DHCP, DNS just regular Domain Controllers. I am wanting to upgrade both servers to 2008R2. What would be the best plan to get these upgraded? I would like to avoid fresh installs on both servers since availability is critical since we are an active hospital open 24/7 and cannot have the servers offline for too long. I have heard in place upgrades are also not the best way to go since there can be quite a bit of cleanup after the upgrade is complete? Should I take down the secondary DC, run soley on server 1 while I do a fresh install on server 2. Once server 2 is ready to go, dcpromo it migrate everything from server1 to it and then take down server 1 for a fresh install and then dc promo it back and pull the roles back from server 2? Which would leave us running a single DC server at all times? The tricky part I forgot to mention is that server1 is also a file server for all AD users home directories which would mean transferring all network resources over to server 2 and modifying the group policy to redirect the workstations where to locate mapped drives, etc. I do have a virtual environment that I could try to transfer the physical hardware to a vm environment temporarily while the physical servers get upgraded and then transfer from vm back to physical using dc promo and other migration techniques? Any suggestions would be much appreciated. I would like to hear that inplace upgrades are safe but there are alot of admins recommending against this approach.