Active Directory secondary domain controller

Question

How can I configure Directory Services (I have Active Directory) with more than one domain controller? Is it correct to add one configuration entry per domain controller? 
 
 Thanks

Domenico Bisesi · Accepted Answer

Thank you for the reply. 
 Searching into documentation I found this: 
 In the Server text box, enter the fully qualified hostname of the server used for directory services look-ups. 
 Alternatively, enter a comma-separated list of failover servers.The first in the list should be the primary server. If the primary server fails, the appliance will attempt to use the other specified servers in the order that they are named. 
 
 Important 
 If you specify multiple servers, you must ensure that each of the servers uses an indentical directory structure. Failure to do so could result in unexpected behavior.