Currently, restoring Read-Only Domain Controllers (RODC) from backup during the Forest Recovery process is not supported.
The only supported recovery methods for RODCs are:
- Restore SYSVOL - This method allows you to perform the non-authoritative restore of RODCs
- Reinstall Active Directory or Reinstall Active Directory from Media on the RODCs
- Install Active Directory or Install Active Directory from Media on the RODCs
- Uninstall Active Directory from the RODCs.
- Do not recover the RODCs.
It is still best practice to install the FR agent on all DCs to ensure that you can configure the required recovery methods.
If you want to recover a read-only DC, you need to select the Install the domain controller as a read-only option on the General tab for the Install Active Directory (with IFM option) or Reinstall Active Directory (with IFM option) method in Forest Recovery Console. A read-only DC can be installed using a backup created only from the RODC. Depending on whether the option is selected or not, you can only choose backups that DC Type corresponds to the type of domain controller (ReadOnly, Writable).
NOTE:
DC Type of backups that were created in the version 10.0 or earlier, and was registered manually, will be shown as Unknown. Such backups can only be selected manually, and the user must make sure that the type of domain controller being restored matches the type of domain controller for which the backup was created, otherwise, recovery of the domain controller will fail.
Based on the above, to be able to use any of these restore methods (other than Uninstall and Do Not Recover) I think a backup is needed for the FR project to be able to do any work against the RODCs.