Recovering Active Directory
Natively AD is backed up by backing up the 'System State'. Pre-Windows 2008 this is achieved through NTBACKUP. On Windows 2008 onwards it is achieved though 'Windows Backup'.
The AD restore procedure involves building a new DC as the first DC in a forest (organisation) and then performing an authoritative restore on it. The loss of a DC should always be recovered by rebuilding the DC if there are other live DCs in the environment.
Disaster Recovery of Active Directory
If there are no DCs available for a domain: Rebuild a DC as the first DC in the domain or forest, whichever is appropriate. An authoritative AD Restore must then be performed.
Authoritative AD Restore
- An AD (system state) backup that is >60 days old cannot be restored as the tombstone interval will have expired.
- This should only be attempted in the event that *ALL* DCs are lost. If non-authoritative/authoritative restore is attempted in an existing forest major replication problems will occur.
- Perform the restore process whilst NOT connected the to the network, and only reconnect when mentioned below.
- No previous DCs should be connected to the network post this procedure.
- Restart DC in Directory Services Restore Mode
- Restore System State through NTBackup ensuring that network adapter details, drive letters, computer name and SYSVOL data locations are identical to the server that the system state backup was taken from.
- Once finished, again reboot into Directory Services Restore Mode and verify the following regkey: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NTDSRestoreInProgress . If should be set to "1" despite the process having finished in reality. This key indicates to NTDS that the AD data is invalid due to it being out of date further to a restore and to instruct it to perform the required steps make it usable. It some scenarios it could be set to "0" but the primary requirement is that the key exists. If it does not then the restore has failed and must be re-attempted.
- Set the AD DB to be the authoritative for the forest:
- Reboot into Directory Services Restore Mode
- Start > Run > ntdsutil
- authoritative restore <enter>
- Restore database <enter>
- Reboot into normal and connect to the network and pray.