The Microsoft Active Directory Migration Tool (ADMT) is a free utility administrators can use to move Active Directory objects, such as computers, users and groups, from one Windows Server Active Directory domain or forest to another.
Administrators use ADMT for crucial changes in the Active Directory environment, such as changing domain names, merging or consolidating domains, or optimizing the arrangement of Active Directory objects in the Active Directory structure. IT may need to change the Active Directory environment to accommodate a merger, acquisition or divestiture within the business as users and systems are added or removed. For example, the IT staff could use ADMT to migrate a 40,000-user environment spread across 50 Active Directory domains to a single domain. ADMT includes wizards that can automate migration operations, but administrators can also perform ADMT operations through the ADMT console, or the command line or with a script.
An Active Directory migration can be a complex process that, if done wrong, can cause disruptions in an organization. As a best practice, administrators should perform extensive pre-migration testing. For example, creating, migrating and verifying access for one or more test users can help reveal issues before administrators make changes in production.
Microsoft developed ADMT to speed the migration process and reduce the chance of errors. ADMT performs object migrations and security translations in a way to limit disruptions to let users access network resources while the migration is underway.
Administrators can install ADMT on any supported version of Windows Server that includes a user interface. Source and target domain controllers must be writable and must be running at an Active Directory domain functional level of Windows Server 2003 or later. Any version of SQL Server can run the ADMT database.