Should preferred Domain Controllers (DC) be specified for the Directory Synchronization Agent (DSA)? How do I set the preferred Domain Ccontroller for the DSA?
It is required that you always specify the preferred domain controller and the preferred Global Catalog server for each Directory Synchronization Agent, and that these be located in the same site as the agent. In addition, we recommend that you set the Directory Synchronization Agent to always use the same Domain Controller and Global Catalog in the domain, as;
1. This ensures, first of all, that the agents will not work with domain controllers and Global Catalog servers located in remote sites across WAN links.
2. The Directory Synchronization Agent uses Microsoft’s Dirsync control to query for directory changes, and Dirsync’s behavior is not consistent when different domain controllers are used to query for changed objects. This issue with Dirsync may have an undesired effect on the Directory Synchronization Agent performing delta sync: if a domain controller from which the agent used to retrieve information about the objects modified since the last session becomes unavailable and no preferred domain controller is set, the agent will be automatically redirected to another domain controller. The new domain controller may return many more objects (or even all objects from the directory) as modified, causing the agent to perform unnecessary jobs
Microsoft describes the issue as follows:
"For incremental searches, the best practice is to bind to the same Domain Controller (DC) used in the previous search, that is, the DC that generated the cookie. If the same DC is unavailable, either wait until it is, or bind to a new DC and perform a full synchronization. Store the DNS name of the DC in the secondary storage with the cookie. You can pass a cookie generated by one DC to a different DC hosting a replica of the same directory partition. There is no chance that a client will miss changes by using a cookie from one DC on another DC. However, it is possible that the search results from the new DC may include reported changes by the old DC; in some cases, the new DC may return all objects and attributes, as with a full synchronization."
MSDN Library info - Polling for Changes Using the DirSync Control - http://msdn.microsoft.com/en-us/library/ms677626(VS.85).aspx
To specify preferred DC and GC for DSA:
1. Select Tools | Agent Manager and select the computer where DSA is installed.
2. Right click and select Properties and check if there are any settings for Preferred DC and Preferred GC.
3. Put hostname values in both columns for both Domains.