I have an old domain server setup as a single DC running Server 2008 R2, and I'm trying to raise the forest functional level to add a new Server 2019 as the domain controller. However, when I attempt to raise the forest level, I get an error message saying: "The functional level could not be raised. The error is: The directory service encountered an unknown failure." I've added another 2008 R2 server as a backup DC in the meantime, and I'm planning to move the FSMO roles to this new server and demote the original one. All DC diagnostics, DNS checks, and replication seems fine, but the Event Viewer isn't showing anything useful. Has anyone encountered a similar issue?
3 Answers
It sounds like you're on the right track, but first, make sure your replication is in good shape. Are you still using FRS for replication? You should have at least two healthy DCs in your environment to do this smoothly. If you have added the second 2008 R2 server and switched to DFRS and replication is passing, you're better positioned for the upgrade.
You're correct about needing all domain controllers to be at least Windows Server 2008 R2 to raise the forest functional level. Here’s a suggested approach:
1. Make sure all DCs are running at least 2008 R2.
2. Backup your DCs before making any changes.
3. Prepare a new Windows Server 2019 machine and promote it to a DC.
4. Once everything's set, go to Active Directory Domains and Trusts to raise both the domain and forest functional levels. Don't forget to demote your old DCs after upgrading!
Yes, it's true that you can't raise the forest level unless all DCs are above the current level in the forest. If you're showing a forest level of 2000, that means you'll need to upgrade all remaining DCs to at least 2008 R2 before raising the level.
Exactly! And just a reminder: After the upgrade, ensure all FSMO roles are transferred to your new DC.