Ransomware-Resilient Backup for a 400 TB CIFS File Service
A 400 TB CIFS file service on an OceanStor 9000 serves 500 finance users. Backups run nightly to a tape library and finish in 6 hours. Last month an attacker used a stolen domain-admin account to delete a 5 TB project folder and encrypt files on a mapped drive; the tape copy was intact but restore of the folder took 19 hours. The business now requires RPO 1 hour, RTO 4 hours for any folder up to 5 TB, 30 daily and 12 monthly restore points, and protection against deletion of backups by a compromised admin. The existing tape library is at end of life. A new OceanProtect backup storage system and a second network segment are approved, but the team cannot change the production CIFS namespace this year. Design the protection.
1. Design layered protection for the 400 TB CIFS service. Explain why snapshots alone are not enough.
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Use three layers. First, array snapshots of the file system every hour with short retention, for example 24 hours, to meet RPO 1 hour and fast restore of accidental deletion. Snapshots are fast, but they remain on the same array and can be deleted by a compromised array admin. Second, daily backups to OceanProtect with 30 daily and 12 monthly restore points, plus a retention policy that the production admin cannot delete. Third, an immutable, air-gapped, or offline copy for the monthly tier, and a protected backup catalog.
Because the attack used domain-admin credentials, assume the production identity plane is compromised: separate backup credentials, MFA, RBAC, and a dedicated backup network. Snapshots alone are not enough because they share the array's admin and security domain and capacity; if the attacker deletes the source and snapshots, there is no independent copy. Tape was independent but too slow for RTO 4 hours. OceanProtect should provide fast restore, while the monthly immutable copy protects against backup deletion.
Do not change the CIFS namespace this year; use existing share paths and array-side snapshots. The layers must not depend on the same administrator account or the same management network.
2. How would you configure backup access and retention so a stolen domain-admin account cannot destroy all copies?
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Separate the backup infrastructure from the production domain where possible: a dedicated backup service account, not a domain admin; MFA for backup console access; role-based access with least privilege; and a separate management VLAN or firewall rule so production admins cannot reach the backup console. On OceanProtect, enable retention lock or immutability for the monthly tier and protect the backup catalog with its own credentials.
Use two-person approval for deleting backup sets or changing retention. Keep at least one copy offline or in a vault that requires a separate process. Monitor and alert on mass deletes, retention changes, and unusual restore activity. If the backup server is domain-joined, limit its domain privileges and use a scoped service account. Test that a production admin cannot delete the backup set.
The goal is not just encryption; it is preventing an authenticated attacker from deleting or encrypting the backup. Document break-glass accounts and store credentials outside the production domain. Also test that restoring from the immutable copy does not require the compromised domain account.
3. What restore validation would prove the RTO of 4 hours for a 5 TB folder?
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Run a timed restore of a real 5 TB folder from OceanProtect to a staging CIFS share, not a file-level sample. Record start and end, throughput, and application validation. Test three cases: accidental deletion restore from snapshot, restore from daily backup, and restore from monthly immutable copy.
For the 4-hour RTO, calculate the required restore throughput: 5 TB in 4 hours is roughly 350–380 MB/s average, so the backup network, target array, and CIFS server must sustain that with overhead. If not, the RTO is not met. Restore to a different path first, validate permissions and file count, then cut over. Include catalog lookup time and any offline retrieval.
Test with backup traffic and production traffic present. Document the runbook and the actual time. Repeat after any change to network, backup policy, or array. A successful backup job is not evidence; only a timed restore is.