DC Upgrade

Getting ready to upgrade our 2008 R2 DC's to 2012 R2.  Five of the eight servers are replacement servers (newer/better equipmnent).  I have the OS's installed on the new equipment.  My next step is to complete the ADPREP commands (forestprep & domainprep) and was wondering what the ramifications are of the commands.  Does this affect the other domain controllers in any way, i.e. what might it screw up?  In the event that something blows up, is there a way to downgrade?  I'm just trying to understand  the process and be prepared, in the event...

Current Environment
8 DC's - Domain & Forest functional level 2008 R2

Upgraded Environment
8 DC's - Domain & Forest functional level 2012 R2
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Cliff GaliherCommented:
Yes, adprep changes the AD database. And since AD is multimaster and changes are synced, the other DCs will be impacted.

As such, while it is considered a low risk operation, backups are still highly recommended, as is knowing how to restore an authoritative AD backup in the event of a significant failure. That is the only officially supported way to downgrade/roll back changes.

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Will SzymkowskiSenior Solution ArchitectCommented:
With AD 2012 adprep is done automatically when you promote your DC, so you should not have to run the commands before hand. This helps in the event that you fat finger something.

Also make sure that your account is part of Schema/enterprise and domain admins group before proceeding.

Also it is a very good idea to make sure that your replication and DC health is clean before doing this. Use the following commands below....
- repadmin /replsum
- repadmin /showrepl
- repadmin /bridgeheads
- DCDiag /v

Once you have confirmed that replicaiton is good then start the process. Also, take system state backups before proceeding.

fcsITAuthor Commented:
Cliff...Thanks for the info, I appreciate it!

Will...on the commands; Everything I've read tells me since my current DC's are 2008 that I need to mount my 2012 installation disc on my current DC's (2008) and run the commands.  Thanks for the commands too!
David Johnson, CD, MVPOwnerCommented:
you can run adprep manually but the server that you are promoting will run it when you promote it.
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Windows Server 2012

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