Recovery Manager for AD Disaster Recovery Edition 10.2.2 - User Guide

Forest recovery approaches

Before you choose one of the recovery approaches described in this section, it is strongly recommended that you read Microsoft’s best-practice paper, Active Directory Forest Recovery Guide.

This section covers the following:

• Recovery approach 1: Restore as many domain controllers from backups as possible

• Recovery approach 2: Restore one domain controller from backup in each domain

Recovery approach 1: Restore as many domain controllers from backups as possible

To use this approach, 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, Approach 1 includes the following stages:

1. Recovery Manager for Active Directory 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.

2. Recovery Manager for Active Directory uses Microsoft 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.

3. The domain controllers where Active Directory was reinstalled replicate AD data from the domain controllers restored from reliable backups.

Approach 1 has the following advantages and limitations:

Advantages

• Fast recovery of the entire forest. Since most domain controllers are simultaneously restored from backups, the forest recovery operation completes faster than in Approach 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 approach 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.

Limitations

The risk of reintroducing corrupted or unwanted data is higher than in Approach 2. Because of the large number of backups used in this Approach, there is no guarantee that corrupted or unwanted data from the backups will not be reintroduced into the recovered forest.

For a step-by-step procedure on how to perform a forest recovery, Overview of steps to recover a forest

Recovery approach 2: Restore one domain controller from backup in each domain

This recovery approach is recommended by Microsoft® in the Planning for Active Directory Forest Recovery paper. To use this approach, 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 approach includes the following stages:

1. Recovery Manager for Active Directory restores one domain controller in each domain from the recent and trusted backup you specify.

2. Recovery Manager for Active Directory uses Microsoft® 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.

3. The domain controllers on which Active Directory was reinstalled replicate Active Directory data from the domain controllers restored from reliable backups.

Approach 2 has the following advantages and limitations.

Advantages

• Recommended by Microsoft. This recovery approach is recommended in the Microsoft’s best practice paper, Planning for Active Directory Forest Recovery.

• Safer, healthier recovery as compared to Approach 1. The limited number of backups used in Approach 2 (one backup per each domain) allows you to check them all to make sure they do not include any corrupted or unwanted data.

Limitations

• Forest recovery may require significant time to complete. Approach 2 requires more time to complete than Approach 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.

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.