currently have a domain controller running Win 2003 SBS, acts as file and print server too. Want to replace it, so I bought a Windows 2012 Std server, 64 bit. I powered it up, did all the Windows updates, antivirus, all the std stuff to get it ready and I plugged it into my network switch. I was able to easily join this to my domain, and reboot and log into my domain account. I can see and PING the current DC as well as the Win 7 client PCs. SO far so good. Now I need to assign roles to it and promote it to a DC. I was reading an article on how to do this and it said the first step is to ensure your current DC is at domain functional level 2003 or better. So I did that and the current DC is only at level Windows 2000 Native. It gives me the option to raise it to Windows Server 2003 but it also says its irreversible, which scares the he4ck out of me because I cannot bring my office of 20 employees to a halt if raising this screws things up. I don't want to end up with a broken DC and a brand new one that hasn't even been set up yet.
I assume the current DC needs to be at level 2003 or better so when I promote the new DC it can "talk" to it and replicate things, that is my guess anyway. So my question is, should I go ahead and raise the level of the existing DC to 2003 from 2000 or does someone know a good reason not to.