I have a client whose AD forest has two trees. The forest root domain is a Windows 2003 domain, another tree is a Windows 2008. Now they are planning to upgrade to domain 2016.
The 2003 domain exists merely because that it's the forest root domain. In fact, all production resources are already in the 2008 domain.
I was wondering if they should create a new forest with a fresh setup 2016 domain, then migrate everything from the other forest to the new domain; or they should setup another tree within the same forest?
Which approach is least interruptive to the production environment?