Active Directory recovery options
Recovery Manager for Active Directory (RMAD) enables the fast recovery of Active Directory® from a disaster. The flowchart below indicates the most suitable recovery method depending on the type of disaster, which could be data corruption, database corruption, or complete Active Directory® corruption.
Data corruption occurs when directory objects have been inadvertently deleted or modified, and the deletion or modification has replicated to other domain controllers within the environment.
Database corruption refers to a situation in which an Active Directory® failure prevents a domain controller from starting in normal mode, or a hardware problem such as hard disk corruption on a domain controller.
RMAD offers the following recovery methods:
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Granular online restore
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Complete offline restore
Granular online restore allows you to restore individual directory objects from a backup, without restarting the target domain controller or affecting other directory objects. It will not be necessary to shut down the domain controller in order to perform the restore: it remains online and functional throughout the recovery.
Complete offline restore only allows you to restore the entire Active Directory® database on a domain controller while Active Directory® is offline. To take Active Directory® offline, RMAD restarts the domain controller in Directory Services Restore Mode (DSRM), resulting in a period of downtime. In addition, complete offline restore affects all directory objects on the target domain controller, which may result in the loss of some of the most recent updates.
All restore operations are remotely administered, so there is no need for an administrator to be physically present at the domain controller.
Granular online restore
To achieve near-zero downtime when recovering Active Directory®, RMAD provides the granular online restore method. Two options are available with this method:
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Compare, restore, and report changes in Active Directory®. With this option, you can restore particular objects from a backup, and select the necessary objects based on a per-attribute comparison of the objects in a backup with those in Active Directory®. Comparison reports are also available.
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Compare two backups and report differences. With this option, you can make a per-attribute comparison of the objects in two Active Directory® backups. Comparison reports allow you to view the object modifications made in the period between the backups.
For details, see Using granular online restore.
Undeleting (reanimating) objects
With RMAD, you can selectively recover deleted Active Directory® objects by undeleting (reanimating) them. To undelete (reanimate) an object, RMAD fully relies on the functionality provided by Active Directory®, therefore to use this method you need no Active Directory® backups. Note that you can only undelete objects in an Active Directory® forest whose functional level is higher than Windows 2000.
For more information, refer Managing deleted or recycled objects.
Complete offline restore
You can use complete offline restore to restore the entire Active Directory database from backup media without reinstalling the operating system or reconfiguring the domain controller. The restore can be performed on any domain controller that can be accessed remotely. By default, this operation restores all directory objects on the target domain controller non-authoritatively. This means that the restored data is then updated via normal replication. A non-authoritative restore is typically used to restore a domain controller that has completely failed due to hardware or software problems.
For details, see Using complete offline restore.
Implications of the online restore
This section provides important information that you should consider when using the Online Restore Wizard.
The wizard allows you to selectively restore a portion of the Active Directory® domain naming context. At that, the wizard causes Active Directory® to replicate this restored state of objects, overwriting the copies currently held on all domain controllers within the domain. The restored objects and object attributes receive a version greater than the current set of directory objects. As a result, the restored objects appear to be more recent and therefore they are replicated out to the other domain controllers within the domain.
Restore the wizard performs is authoritative. With an authoritative restore, Active Directory® object data reverts to the state it had when the backup was created and any updates that were made after that point are lost. For example, obsolete passwords could be restored, which may have impact on user and computer accounts.
One more issue related to authoritative restore is the impact on linked attributes, such as group memberships. For example, when you authoritatively restore a user that is currently marked as deleted (undelete a user account), in some recovery scenarios you risk possible loss of group membership information.
To ensure the correct restoration of group memberships, along with the other linked attributes, the Online Restore Wizard can force incremental replication of Active Directory®. Incremental replication transfers only the changes that occurred since the last replication.
Once the wizard has undeleted some objects for which linked attributes need to be restored, it reminds you that the un-deletion must be replicated to all domain controllers for the linked attributes to be correctly represented on each domain controller. The wizard prompts you to choose whether to force the replication, skip the replication, or stop the operation.
Before making a choice, consider the following:
Forcing replication
When you choose to force the replication, the wizard ensures that all linked attributes, such as group memberships, of the undeleted objects are correctly restored on all domain controllers.
This choice may result in considerable replication traffic, depending on the number of domain controllers in your domain. However, it is required because of the way links and deletions are dealt with in Active Directory®. Before the restoration of linked attributes, the undeleted objects must be replicated to all domain controllers for the restored linked attributes to be correctly represented on each domain controller.
This requirement stems not from the wizard’s implementation, but from the way in which the data is replicated in Active Directory®.
Skipping replication
When you choose not to force the replication, you may risk a loss of linked attributes, such as group memberships, on replication partners after the normal Active Directory® replication transfers the undeletion to all domain controllers.
For example, when you select a user to be undeleted, with the user being a member of a certain group, and choose not to have the wizard force the replication, the results of the restore on the representation of the user’s group memberships may vary. These variations are based on which objects replicate first after the wizard completes the restore.
If the undeletion of the user replicates first, then the group membership information of both the group (the members it contains) and the user (the groups he or she belongs to) will be represented correctly.
If the restore of the group replicates first, the replication partners will drop the addition of the (locally) deleted user from the group membership. The only exception to this is the user’s primary group, which is always represented correctly from both the user and group reference.
The wizard marks the undeleted objects so that they are replicated in a proper sequence. However, making changes to them before the replication is completed may break the proper sequence. Skip the replication enforcement if you are sure that no changes will be made to the restored objects until those objects are replicated to all domain controllers within the domain. Optionally, you may have the wizard force the incremental replication on the final step. You might also force the replication with a different tool, or wait for replication to occur on normal schedule.
In addition, you might skip the replication enforcement if you undelete objects whose deletions are not yet replicated within your domain. In that scenario, the objects in question are not marked as deleted on other domain controllers, which ensures the correct representation of linked attributes.