I'm building and testing an Active Directory backup and recovery process for an environment with more than 20 domain controllers, all running as Hyper-V or VMware virtual machines. I'm aiming to follow the 3-2-1 backup strategy.
Our primary backup platform is Dell Avamar, which supports bare-metal recovery and system-state backups. My current plan is to back up system state in addition to the VM-level backups already protecting two domain controllers. For a second backup copy, I'm considering Azure Blob Storage using the Cold tier, with either the Microsoft Azure Recovery Services agent or an Azure CLI-based process.
I'd appreciate feedback on several points:
1. If the Avamar management infrastructure is joined to Active Directory, would a domain compromise also put the backup system at risk? Should the backup platform use standalone credentials or a separate management forest instead?
2. Is Azure Blob Cold storage suitable for this type of backup, considering retrieval delays and early-deletion or minimum-retention charges?
3. Which recovery scenarios should be tested in an isolated network? Should I practice a full forest recovery, a single-domain recovery, an authoritative restore, or a specific GPO and SYSVOL restoration? Active Directory Recycle Bin is already enabled.
4. Besides the built-in Administrator account, which credentials and recovery accounts should be regularly validated, especially the Directory Services Restore Mode account?
I'm looking for practical guidance on the design, security controls, and recovery tests that are commonly used in production environments.
4 Answers
The recovery credentials worth validating include the DSRM local administrator account on every domain controller, the designated forest and domain recovery accounts, backup-platform break-glass accounts, and any credentials used by the recovery environment. Test that the accounts work without depending on normal domain authentication. Keep the passwords in a secured vault and verify that the recovery team can retrieve them during an outage. A practical test is to restore a controller into an isolated network, boot into DSRM, recover AD, bring up DNS and SYSVOL, and verify logons, replication, GPO processing, and important services.
For a complete loss scenario, practice forest recovery rather than restoring every domain controller from VM snapshots. In an isolated network, restore one suitable domain controller from system state, perform the required authoritative recovery steps, identify or seize the FSMO roles as appropriate, and then rebuild or restore additional controllers carefully. You should also test metadata cleanup, SYSVOL and GPO recovery, DNS, authentication, and application dependencies. Be cautious with ordinary VM snapshots or rollbacks of domain controllers because they can create replication problems such as lingering objects or USN-related issues.
Cold storage can be appropriate for an inexpensive secondary or archival copy, but account for retrieval latency, minimum-retention requirements, and early-deletion charges. I would keep at least one recent recovery point in a faster tier so a routine restore does not depend on rehydrating cold data. Whatever storage you choose, use immutability or object lock, encryption, separate administrative access, and monitoring that alerts when backup jobs or retention settings are changed.
Keeping the latest restore point in a warmer tier while using Cold storage for longer-term retention sounds like a good compromise.
The backup control plane is the biggest concern. If the backup management server or appliance authenticates directly against the same AD it protects, an attacker who compromises the domain may be able to disable jobs, delete catalogs, or destroy the recovery path. Keep the backup infrastructure outside the protected domain when possible, use separate local or vault-managed credentials, restrict administrative access, and make at least one backup copy immutable and isolated. A separate management forest can also work. System-state and VM backups are useful, but neither replaces a rehearsed forest-recovery procedure.
That makes sense. I’ll look at separating the backup management plane and ensuring the off-site copy cannot be altered using compromised domain credentials.
Also document which domain controllers hold the FSMO roles and where the DSRM passwords are stored. Those details are easy to overlook until a complete outage occurs.