How to set a preferred DC in PowerShell
It’s quick and easy but keep in mind this does not set a default for PowerShell sessions. You’ll have to enter this command in each window you want to specify a DC in.
Set-ADServerSettings –PreferredServer <fqdn>
On the same subject, it’s easy to find out what DC & GC you’re using in a particular PowerShell session. Just execute the following command:
Get-ADServerSettings | fl