In our building, we have two separate subnets of private IP's. The first and second floors of our building use IP addresses in the 192.168.1.0/24 range and the third floor uses IP's in the 192.168.3.0/24 range.
Our network is an Active Directory network using a combination of Windows Server 2008 R2 and Windows Server 2012 R2 servers. All clients are Windows 7 Enterprise x64 clients. We currently have DHCP and DNS servers on each subnet, but our two domain controllers are both on the 1.0 subnet.
My question: Is it good practice to have a domain controller one each of the two subnets to minimize the amount of traffic that is having to be routed between them as people log in? Are there any potential drawbacks to placing a domain controller on each subnet? Is there really going to be a performance benefit to having one on each network?