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I have two servers. One is primary DC, another is ADC. Now the primary DC got crashed. ADC is serving the purpose now.
I need to format the Primary DC server to make it up. After installing the OS, how i need to bring it in domain as Primary DC??
Shall I add as ADC to the running one?

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There is no such thing as a "primary" domain controller any more. There are just "domain controllers", one of which can hold the PDC role for legacy applications... – Mark Henderson Jun 29 '12 at 1:29
I am using Windows server 2003 R2. So shall I add the new one as ADC?? – Olivarsham Jun 29 '12 at 1:33
What do you mean by "ADC"? I've never seen that term before. You have "domain controllers", and have had for about 13 years. If a domain controller fails, you can either restore it from a Microsoft-sanctioned backup routine (that's critical for a domain controller), or you build a new, fresh machine and promote it to being a DC. If the only thing your domain controller was doing was being a DC (i.e. it wasn't running DHCP or WSUS or anything except AD and DNS) then just build a fresh machine, and promote it to a Domain Controller. Job done. – Mark Henderson Jun 29 '12 at 1:36
No offense but it sounds like you are way over your head here. I suggest you request an emergency budget to hire someone with the expertise to get your environment fixed now. A crisis is a bad time to learn. – kce Jun 29 '12 at 1:37
ADC = Additional Domain Controller??? – HopelessN00b Jun 29 '12 at 2:01
up vote 5 down vote accepted

Seize the PDC Emulator role (and any other relevant roles) from the dead domain controller - instructions on this process are here.

Once that's done, you'll probably also want to clean up the dead domain controller's metadata from the domain before trying to re-promote the server again with the fresh OS. Here's the documentation for that process.

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In a 2008 R2 DFL (which is sounds like the OP might have) the metadata cleanup process is as easy as deleting the dead DC computer object from AD. – MDMarra Jun 29 '12 at 1:36
Nevermind, I misread the OP's comment. I can't read, apparently :) – MDMarra Jun 29 '12 at 1:43
@MDMarra With sufficiently bad font kerning, 3 == 8. ;) – Shane Madden Jun 29 '12 at 1:49

There are no such thing as an ADC or PDC. They are all multimaster peers. Please read this.

If the DC that crashed held any operations master roles, then you need to transfer them to the other DC. Clean up the metadata for the dead DC by following these steps. Then, reinstall the crashed server and promote it using dcpromo and you're done.

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