First off, leave the Sysvol (aka "Domain System Volume") DFS replication entry alone. That's a normal function of AD and doesn't need any tweaking from the defaults.
As for the file server, there are two separate DFS-related technologies in play here, the DFS Namespace which is responsible for hosting the actual shares and DFS Replication which only cares about making sure the data is synchronized between your DC and the Fileserver. One doesn't require the other and they can run separately with no problem.
So, first step is to examine your DFS Namespace. There's likely at least one folder/share defined in there. Select each one and do the following.
- Check the Folder Targets tab. There should be at least one entry pointing to your file server. If there's only the one entry, great. You're done.
- If your DC is listed in the Folder targets and it's not the only entry, delete it. This won't break existing client connections. But it will stop new clients from being directed to it.
- If your DC is listed and it is the only entry, you've got two steps. First, add a new entry pointing to your file server and wait until you start seeing clients get directed to it. Then delete the entry for the DC.
- If you made any changes, start monitoring the share's connections until everyone has filtered off the DC.
Now that no clients are actually using the DC as a file server, you can move on to DFS Replication.
- Select the replication group and go to the Memberships tab
- Remove the entry for your DC
- If you're going to stop using DFS Replication entirely, you can also just delete the whole replication group. But if you're planning on bringing up a new backup file server, you may want to just keep it and add the new server later.
- The DFSR service on the DC will eventually pick up the changes on its own or you can manually restart the service.
- There will be some messages in the DC's DFS Replication event log indicating it has picked up the changes and removed itself from the group. At that point, it's safe to delete the data.
Update
Your comment made me realize I forgot to talk about the Namespace Servers themselves. So the way DFS Namespace's work is that a set of servers "host" the root namespace (e.g. \\example.com\ns
) so that when people are looking for a specific share like \\example.com\ns\share
, they effectively get routed to one of the servers hosting that share by asking a one of the namespace servers.
You mentioned that in your namespace, both the file server and the DC are listed in Namespace Servers for your namespace. There's no harm in leaving that as-is. And having two available means that clients won't throw errors trying to connect when one is down for patching and such. I commonly see people use multiple DCs as namespace servers.