There is no concept of primary/secondary/backup or master/slave in 'Active directory' environment. Any new domain controller will act as an additional DC.
Active Directory uses multimaster replication, which means all DCs will have same data across. Additional domain Controllers provide redundancy.
I do not represent the organisation I work for, all the opinions expressed here are my own.
This posting is provided AS IS with no warranties or guarantees and confers no rights.
Proposed as answer byMeinolf WeberThursday, April 25, 2013 8:58 AM
Microsoft is conducting an online survey to understand your opinion of the Technet Web site. If you choose to participate, the online survey will be presented to you when you leave the Technet Web site.