Forest recovery methods
Before you choose one of the recovery methods described in this section, it is strongly recommended that you read Microsoft’s best-practice paper, Planning for Active Directory Forest Recovery.
This section covers the following:
Recovery method 1: Restore as many domain controllers from backups as possible
To use this method, you must have recent and trusted backups for as many domain controllers as possible in each domain in the forest. These backups must be created at a similar point in time to mitigate the risk of discrepancy after the forest is recovered.
At a high level, Method 1 includes the following stages:
- Recovery Manager for Active Directory Disaster Recovery Edition restores as many domain controllers as possible in each domain from the recent and trusted backups you specify. The more domain controllers you restore from backups, the faster the forest recovery operation completes.
- Recovery Manager for Active Directory Disaster Recovery Edition uses Microsoft’s native tools (Dcpromo.exe or the Uninstall-ADDSDomainController and Install-ADDSDomainController cmdlets) to automatically reinstall Active Directory on the domain controllers for which no backups are available.
- The domain controllers where Active Directory was reinstalled replicate AD data from the domain controllers restored from reliable backups.
Method 1 has the following advantages and limitations:
Table 33: Recovery method 1: Advantages and limitations
- Fast recovery of the entire forest. Since most domain controllers are simultaneously restored from backups, the forest recovery operation completes faster than in Method 2.
- Stability of the forest recovery process. Owing to the large number of backups used, the entire forest is recovered even if the restore of some domain controllers fails.
- This method allows you to retain the original forest infrastructure. Since many domain controllers are restored from backups, the recovered forest is close to its original prefailure condition.
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- The risk of reintroducing corrupted or unwanted data is higher than in Method 2. Because of the large number of backups used in this method, there is no guarantee that corrupted or unwanted data from the backups will not be reintroduced into the recovered forest.
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For a step-by-step procedure on how to perform a forest recovery, Overview of steps to recover a forest
Recovery method 2: Restore one domain controller from backup in each domain
This recovery method is recommended by Microsoft in the Planning for Active Directory Forest Recovery paper. To use this method, you must have a recent and trusted backup for one domain controller in each domain in the forest. These backups must be created at a similar point in time to mitigate the risk of discrepancy after the forest is recovered.
At a high level, recovering a forest using this method includes the following stages:
- Recovery Manager for Active Directory Disaster Recovery Edition restores one domain controller in each domain from the recent and trusted backup you specify.
- Recovery Manager for Active Directory Disaster Recovery Edition uses Microsoft’s native tools (Dcpromo.exe or the Uninstall-ADDSDomainController and Install-ADDSDomainController cmdlets) to automatically reinstall Active Directory on the domain controllers for which no backups are available.
- The domain controllers on which Active Directory was reinstalled replicate Active Directory data from the domain controllers restored from reliable backups.
Method 2 has the following advantages and limitations:
Table 34: Recovery method 2: Advantages and limitations
- Recommended by Microsoft. This recovery method is recommended in the Microsoft’s bestpractice paper, Planning for Active Directory Forest Recovery.
- Safer, healthier recovery as compared to Method 1. The limited number of backups used in Method 2 (one backup per each domain) allows you to check them all to make sure they do not include any corrupted or unwanted data.
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- Forest recovery may require significant time to complete. Method 2 requires more time to complete than Method 1.
- Recovery of entire domain depends on a successful restore of a single domain controller. A successful restore of one domain controller from backup is required before Active Directory can be reinstalled on all other domain controllers in the domain.
- The original forest infrastructure is not retained. Because Active Directory is reinstalled on most domain controllers in the forest, the forest infrastructure cannot be restored to its exact pre-failure state.
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For a step-by-step procedure on how to perform a forest recovery, Overview of steps to recover a forest
Deciding which backups to use
To restore domain controllers from RMAD or BMR backups, use the backups that were taken a few days before the occurrence of the failure. In general, you have to trade off between recentness and safeness of restored data. Choosing a more recent backup recovers more useful data, but it might increase the risk of re-introducing dangerous data into the restored forest.
It is strongly recommended that you keep detailed logs about the health state of Active Directory on a daily basis, so that in case of a forest-wide failure you could identify an approximate time of the failure.
For more information on the methods you can use to select backups for recovery, see Selecting backups for recovery.
