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2000 to 2008 R2 Migration and Active Directory Database Size Growth

I have 6 2000 DCs and I am planning to migrate to 6 2008 R2 DCs on new hardware.   I plan to introduce my first 2008 R2 DC in the next couple of days.  As you can imagine, our new hardware is wicked fast compared to the old and the new storage is about 40 GB per db/logs/sysvol volumes.

Our current average database size is about 700 MB.  I understand that the 2008 R2 AD database increases by a considerable amount to accomodate changes such as no more partial merge, two new indices on the large link table and if using the AD recycle bin.

This Microsoft Assess Hardware Requirements article leads me to believe our post-migration AD DB size will be 2.8 or roughly 3 GB based on 7500 users.

Here is my problem:  

The article tells me why the size will increase, but it does not tell me *when*.  

This scares the hell out of me as I am afraid that when I bring the first 2008 R2 DC online, our AD DBs will grow to 3 GB on all of the 6 2000 DCs immediately.  

On each 2000 DC volume that currently holds the AD DBs,  is limited space (by today's standards)...

DC1 - 9.3 GB
DC2 - 9.3 GB
DC3 - 5.3 GB
DC4 - 5.3 GB
DC5 - 5.3 GB
DC6 - 9.3 GB

I worry that when I dcpromo my first 2008 R2 member server to a DC, it will negatively impact my production environment.  I could really use an online resource that answers the question - when will my AD grow?  Thank you.
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Top Expert 2012
Commented:
You will not be able to use the new features until your domain and forest levels are set to Windows 2008 server so you will not get a DB increase until these levels have been moved up. So, until all of  your 2003 DCs are gone you will not have to worry.
Top Expert 2010

Commented:
These 2 sources talk about how to monitor ad using repadmin and dsastat

http://searchwinit.techtarget.com/tip/0,289483,sid1_gci1166462_mem1,00.html
http://blogs.technet.com/b/ad/archive/2009/02/16/gauging-size-differences-in-ad-databases.aspx

There's another one from MS - which says you'd need something like MOM to monitor AD objects.
http://technet.microsoft.com/en-us/library/dd262025.aspx

Also
Please do let us know if you find something useful which monitors the growth of ntdis.dit
Top Expert 2010

Commented:
MOIT Experts
let me know if you managed to figure out the *when* part :-)

Author

Commented:
I buy the answer, but I'd rather have a definitive source.