planning to upgrade from 2003 to 2010 in a coexistence mode. As the best practice suggests: a separated AD site with dedicated domain controller for all exchang 2010 servers is recommended. For example: exchang 2003 servers are in AD site#1 now using DC1 and DC2. If a new AD site#2 with DC3 and DC4 is created for new exchange 2010 servers, can the new installation of exchange 2010 still be able to coexist smoothly with the 2003 server in AD site #1? Which way is more practical for a smooth upgrade from 2003 to 2010? 1. install all new exchange 2010 servers in AD site#1 and set up static Domain controller access to give the new servers dedicated domain controllers.. or. 2.create a new AD site#2 with dedicated DCs and install all new 2010 servers in this new AD site#2. Not sure whether the coexisitence is still possible by this way. thanks

Where have you seen this published as a best practice? It's something worth considering in large organizations, but I think it's unnecessary in smaller organizations. There is no requirement to put Exchange 2010 in a different AD site from Exchange 2003.Ed Crowley MVP "There are seldom good technological solutions to behavioral problems."

Agree with Ed. As its not going to make any changes in exchange. If you install Exchange 2010 in Exchange 2003 site, it would be more easy to implement :) and Migrate. Cheers, Gulab | MCTS-MCITP Messaging: 2010 | MCTS-MCITP Messaging: 2007 | MCC 2011 | Skype: Gulab.Mallah

I don't know that it's necessarily easier to implement and migrate. I don't think it makes much difference except that if you install in a new site you have to build new DCs in the new site or move existing DCs to the new site.Ed Crowley MVP "There are seldom good technological solutions to behavioral problems."

If a separated AD site will be created for exchange 2010 servers, we are going to build two new DCs there. What I worried is this may make the migration difficulty since the new 2010 servers are in different AD site.

Is there any particular requirement for an additional AD site, besides you're bringing up Exchange 2010? If the only reason you're considering a new AD site is because of Exchange 2010 I agree with above posters, and do not suggest it. It complicates routing and replication needlessly. Keep everything together unless there is a specific business requirement to separate them, which doesn't appear to be the case.

Is there any particular requirement for an additional AD site, besides you're bringing up Exchange 2010? If the only reason you're considering a new AD site is because of Exchange 2010 I agree with above posters, and do not suggest it. It complicates routing and replication needlessly. Keep everything together unless there is a specific business requirement to separate them, which doesn't appear to be the case.

There is no need for a separate site. If you do create a separate site, it should not complicate your transition. Don't worry about it.Ed Crowley MVP "There are seldom good technological solutions to behavioral problems."