We have a resource forest set up.
We have resource domain, where all resource, such as mailboxes, file/print servers are kept and there is user domain, where only user accounts are kept.
User account in resource domain is disabled. Mailbox is linked to user account in the user domain. This is done by LinkedMasterAccount attribute in the user account.
we have 1 hub and client access server ( which is also DC) and 1 mailbox server sitting on xxx. lan domain which is in resource domain.
We have another DC which is xxx.com which have all enabled accounts.
We have 2300 users and divded into 16 storage groups
We are planning to upgrade to exchange 2013
Our Action Plan
A) We want to keep the same resource setup.
B) Build separate windows server 2012 and make it DC in same resource forest set up
C) Replicate DC from exchange 2007 ( CAS and Hub Server) to new windows server 2012 DC as disabled AD accounts.
D) Install exchange 2013 on windows server 2012 and build DAG involving 3 mailbox servers
E) Move mailbox from exchange 2007 to 2013
Please add to my plan if I am missing something