Active Directory, Second Edition

Data Replication

Microsoft has introduced a number of new terms for Active Directory replication, and most of them will be completely unfamiliar to anyone new to Active Directory. To properly design replication, you need to understand how replication works, but more to the point, you need to understand how replication works using these new terms, which are used throughout both Microsoft’s documentation and its management tools. Here is the list of the terms you’ll encounter as we explain replication. These definitions will make more sense later.

Update Sequence Number (USN)

This 64-bit value, which is assigned to each object, increments every time a change takes place.

Originating write/update and replicated write/update

A change made to an object on a specific DC is an originating write; replication of that change to all other DCs is a replicated write.

High-Watermark Vector

This USN represents the maximum number of changes ever to occur on a particular NC.

Up-To-Date Vector

This is the USN on a specific server that represents the last originating write for an NC on that server.

Tombstone

Because of the complex replication available in Active Directory, simply deleting an object could result in it being re-created at the next replication interval, so deleted objects are tombstoned instead. This basically marks them as deleted. Objects marked as tombstoned are actually deleted 60 days after their original tombstone status setting; however, this time can be changed by modifying the ...