One of the first steps towards simplifying your Active Directory migration is directory normalisation. This process involves re-designing each of your Organisational Unit structures in order that they are identicle in each source domain. This allows you to locate service accounts, generic accounts and resource mailboxes in seperate OUs, thus allowing identification of these resources in advance of the migration. Numbers are important during a migration, so when this process is finished you’ll be able to identify:
1) Number of non-adminisitrative user and computer accounts in each source domain
2) Number of service accounts in the domain
3) Number of generic logon accounts in the domain
4) Number of resource mailboxes in the domain
An example of a normalised OU strufture is as follows:
You can clearly see the division of user and computer objects, Exchange objects (excluding User Mailboxes), service accounts and server objects. This structure allows for simple Group Policy management as well as simplified administration.
By performing the above process on each of your source environments this will speed up the process of migration as the administrators do not necessariliy need to be familiar with the source environments to perform a stream-lined and well-structured migration. Just be careful when moving objects into new OUs as this can change Group Policy inheritance!