The Active Directory Database Garbage Collection Process (198793)

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Garbage Collection is a housekeeping process that is designed to free space within the Active Directory database. In Windows 2000, this process runs on every domain controller (DC) in the enterprise with a default lifetime interval of 12 hours. This interval can be changed by modifying the garbageCollPeriod attribute in the enterprise-wide DS configuration object (NTDS).

For a domain controller named \\Server1 in the Company.com domain, the path for this attribute would be:
Use the Active Directory editing tool of your choice to set the garbageCollPeriod attribute. Supported tools include Adsiedit.msc, Ldp.exe, and ADSI scripts.

The Garbage Collection process starts by first removing "tombstones" from the database. Tombstones are remains of objects that have been previously deleted. (When an object is deleted, it is not actually removed from the Active Directory database. It is instead marked for deletion at a later date. This then gets replicated to other domain controllers. When the time expires for the object (tombstoneLifetime), the object is deleted.) Next, the garbage collection process deletes any unnecessary log files. Finally, the process launches a defragmentation thread to claim additional free space.

In addition, there are two ways to defragment the Active Directory database in Windows 2000. One way is an online defragmentation method that runs as part of the garbage collection process. The only advantage to this method is that the server does not need to be taken offline for it to run. However, this method does not shrink the Active Directory database file (Ntds.dit). Another way is to take the server offline and use Ntdsutil.exe to defragment the database. This approach requires that the DS database be started in repair mode. The advantage to this method is that the database is resized, unused space is removed, and the size is reflected by the Ntds.dit file. The domain controller has to be taken offline to use this method.