Q: What’s the Active Directory Load Balancer tool?

A: With Windows 2000 Server, there’s one bridgehead server per naming context, so under Win2K, no matter how many domain controllers (DCs) are in a hub site, only one would be used for intersite replication. This changed with Windows Server 2003, and intersite replication is now load-balanced over the available DCs in a location; however, this load balancing is performed only initially. If a new DC is added at a location, then existing connections won’t be re-evaluated and spread more evenly between the DCs. Active Directory Load Balancer, which is part of the Windows 2003 Resource Kit tools, solves this problem by load balancing connection objects between the available DCs. The tool runs these three process phases:

  • Gathers data about the sites and connection objects
  • Calculates the new replication connection object design
  • Writes the updated connection object properties

Load-balancing the connection objects between the DCs is useful, but the tool also staggers when replication will occur within the replication interval. For example, if it replicates site A between minutes 0 and 15 of the replication cycle, it then replicates site B between minutes 16 and 30. This is a great feature that spreads out the load experienced by the hub DCs, allowing them to support even more branch sites. Without Active Directory Load Balancer, all replication takes place in the first 15 minutes of a replication cycle.

—John Savill