A domain controllernamed DC12 runs critical services.
Restructuringof the organizational unit hierarchyfor the domain has been completed and unnecessary
objects have been deleted.
You need to perform an offline defragmentation of the Active Directory database on DC12.
You also need to ensure that the critical services remain online.
What should you do?

A.
Start the domain controller in the Directory Services restore mode. Run the Defrag utility.

B.
Start the domain controller in the Directory Services restore mode. Run the Ntdsutil utility.

C.
Stop the Domain Controller service in the Services (local) Microsoft Management Console (MMC). Run the
Defrag utility.

D.
Stop the Domain Controller service in the Services (local) Microsoft Management Console (MMC). Run the
Ntdsutil utility.

Explanation:
http://support.microsoft.com/kb/232122
Performing offline defragmentation of the Active Directory database
Active Directory automatically performs online defragmentation of the database at certain intervals (by default,
every 12 hours) as part of the Garbage Collection process. Online defragmentation does not reduce the size of
the database file (Ntds.dit), but instead optimizesdata storage in the database and reclaims space inthe
directory for new objects.
Performing an offline defragmentation creates a new, compacted version of the database file. Dependingon
how fragmented the original database file was, the new file may be considerably smaller.
http://rickardnobel.se/when-to-offline-defrag-ntds-dit/
When to offline defrag the Active Directory database
This article will show a simple way to determine ifthere is any gain to do an offline defrag of your Active
Directory database.
During normal operations the Active Directory service will do an online defragmentation of the Active Directory
database (always called ntds.dit) each 12 hours. This online defrag will arrange all pages in an optimal way
internal in the ntds.dit, however the file size will never shrink, sometimes even grow. During the years of
operations of the ntds.dit the file size will increase as user accounts, organizational units, groups,computers,
dns records and more are added and later removed. When deleted objects are finally removed (after the so
called tombstone lifetime, typically 180 days) the space they have occupied will unfortunately not decrease.
The actual size of the ntds.dit could be easily studied through Explorer, as above. The size of the database is in
this example around 575 MB. Note that Active Directory does not use a file level replication, so the file could be
of various size on each Domain Controller in your domain. If wanted there is the possibility to take the AD
services offline on one DC and then do an offline defragmentation of ntds.dit. This would both arrangeall pages
the best possible way, and also to reclaim any empty space inside the database, which could make backup and
restore faster and also possible increase AD performance.
The offline defrag means “offline” from an Active Directory perspective. This means that on Windows 2000 and
2003 you will have to reboot into Directory Services Restore Mode, and on Windows 2008 and R2 you willhave
to stop the AD services by typing “net stop ntds” in the command prompt. So in Windows 2008 and later it is far
easier, but still something that you do not want todo if not necessary.
There are numerous article on the web how to do theactual offline defrag, so we will not cover that part here.
However, we will see the perhaps most important information and that is to be able to see in advance the
amount of space that we could reclaim. With this information we could make our decision based on fact and not
guesses. This has been possible since at least Windows 2003, but is not well documented.
To enable this you will have to alter a registry value on the Domain Controller you will investigate the
reclaimable MBs. Use regedit and find the followingkey:
HKEY_LOCAL_MACHINE \ System \ CurrentControlSet \ Services \ NTDS \ Diagnostics
Change the value “6 Garbage Collection” from 0 to 1. This will increase the logging from the Garbage Collection
process which runs together with the online defrag.So now wait for the next online defragmentation which runs
twice a day and then study the Directory Service log in Event Viewer.
Search for event id 1646, usually together with event ids 700 and 701.
Here we can note the amount of space that would be reclaimed from an offline defrag. The top value is the
number of MB that the offline defrag would recover,here almost half the database size. If the amount is
negligible then do not worry about this any more, and if there is a considerable amount of MBs reported then
you could plan to do the offline defrag.
Note that both the change of registry key and the actual offline defrag has to be done on each domain
controller, since neither does replicate.
As noted above we will not look at the commands forthe offline defragmentation here, since they are well
documented already.