If ransomware encrypts a shared file server, how can backups be protected from deletion or encryption at the same time?

Combine immutable copies, offline or isolated copies, separate credentials, least privilege, recovery testing, and alerting rather than relying only on online NAS snapshots.

1. Conclusion and scope

Before troubleshooting, collect the backup product and version, job and repository details, restore points and retention policy, complete errors, capacity and verification status, application-consistency settings, and the result of the latest restore test. No real customer parameters are used.

This issue involves Backup, NAS and business continuity. Logs and configuration can often be collected remotely first. Bulk permission changes, switch-path work, production cutovers, and recovery drills should use a controlled implementation window.

2. Symptoms and business impact

• Capture the complete error text, event-log timestamp, and failed action rather than relying on a verbal description.
• Record the affected scope, first occurrence, reproducibility, and whether the result changes on another subnet.
• Combine immutable copies, offline or isolated copies, separate credentials, least privilege, recovery testing, and alerting rather than relying only on online NAS snapshots.

3. Likely causes and diagnostic checks

1. Keep at least one backup copy that production credentials cannot delete or modify, with a defined immutability period, capacity plan, and emergency recovery process.
2. Disconnect offline or isolated copies from the production network after backup and regularly verify media, catalogues, and recovery keys.
3. Use separate administration identities and MFA for backup servers, repositories, and hypervisors so a compromised domain-admin credential cannot destroy production and backups together.
4. Snapshots depend on the original storage and are suitable for short-term rollback; independent backups must cross devices or failure domains and be recovery-tested.
5. Test full-machine, file, database, and application recovery separately and record RTO, RPO, credentials, network isolation, and acceptance results.
6. Check repository capacity, file-system health, integrity checks, retention chains, synthetic operations, and immutable or offline copies.

# Verify that production credentials cannot delete the protected backup copy.
# Perform an isolated file and full-system recovery test on a scheduled basis.

4. Remediation and controlled rollout

Start with read-only queries, configuration exports, and one-system validation. Once the root cause is confirmed, define the target scope, change window, and rollback method. Include recovery testing in monthly or quarterly operations, rotating full-machine, file, database, and critical-application tests while recording recovery time.

• Snapshots depend on the original storage and are suitable for short-term rollback; independent backups must cross devices or failure domains and be recovery-tested.
• Test full-machine, file, database, and application recovery separately and record RTO, RPO, credentials, network isolation, and acceptance results.
• Check repository capacity, file-system health, integrity checks, retention chains, synthetic operations, and immutable or offline copies.

5. Validation, rollback and common mistakes

Do not stop when the service works once. Revalidate with the user workflow, logs, a restart or fresh sign-in, another network location where relevant, and the next policy or backup cycle.

Validation and rollback checks

• Change one variable at a time and export the current configuration before making changes.
• Test full-machine, file, database, and application recovery separately and record RTO, RPO, credentials, network isolation, and acceptance results.
• Check repository capacity, file-system health, integrity checks, retention chains, synthetic operations, and immutable or offline copies.

Common mistakes to avoid

• Treating a successful job or an existing snapshot as proof of recoverability.
• Running recovery tests on the production network and causing identity conflicts.
• Keeping every copy on the same appliance without an independent or offline copy.