What to do if…

The NAS is not responding

An unreachable NAS is diagnosed like a server: network first, disks next, external copy in parallel. An internal RAID is not repaired by pulling disks out at random: as long as a copy outside the NAS exists, it is your path to restoration, and tinkering with the disks is the path to permanent loss.

Updated October 20263 min read5 sources cited

Key points

Network first: another computer, the admin interface, another cable, another switch. Many “dead NAS” cases are dead switches.
Several disks raising alerts, or unreadable files: stop all writes, do not rebuild blindly.
Volume still readable: copy the critical folders off the NAS first, repair afterwards.
Internal snapshots die with the NAS: only the external copy counts.
A NAS is a source to be backed up, not a backup.

1. See how far the failure extends

Symptom	Probable cause	First step
Only one computer can no longer see it	The computer: network drive, password, VPN	Test from another computer
No computer can see it, nor the admin interface	Network, power supply or frozen device	Ping, status lights, another cable, another switch
The interface reports a failed disk	Degraded volume, still sound if the RAID has headroom	Replace the disk indicated by the manufacturer, not another one
Several disks raising alerts, volume degraded beyond what the RAID tolerates, unreadable files	Loss of redundancy or corruption	Stop all writes, do not rebuild blindly
Files renamed or encrypted en masse	Attack	Disconnect the NAS from the network and follow the ransomware guide

Many “dead NAS” cases are dead switches.

If the files on the NAS have changed extension or display a ransom demand, this is not a failure: disconnect it from the network without shutting it down and go to Ransomware has just struck.

2. Protect what still responds

If the volume is still readable, immediately copy the most critical folders to a disk that is not in this NAS, in addition to the backup already held off-site. Then run the repair recommended by the NAS manufacturer.

A RAID rebuild puts heavy strain on all the remaining disks. If a second disk is ailing, it can destroy the volume: if two disks are doubtful and an external backup is good, restoring from outside is often safer than rebuilding.

3. Restore from the copy outside the NAS

If the volume is dead:

restore the shares from the off-site backup to a new volume, another NAS or a server;
reapply the permissions, or recover them if the NAS configuration was itself backed up;
recreate the tasks and accounts. Without a configuration export, this part has to be redone by hand: it often takes longer than copying the files.

Snapshots internal to the lost NAS are no longer available. NIST puts it this way in its storage security guide: if the source data is unavailable, the snapshots can no longer be used either. Only the copy that was taken outside it is of any use.

RAID, snapshots, external backup: what protects against what

Risk	RAID	Internal snapshots	Backup outside the NAS
Single disk failure	Yes	No	Yes
File deleted by mistake	No	Yes, as long as the NAS is working	Yes
Failure of the NAS itself	No	No	Yes
Ransomware with administrator access	No	Often not	Yes, if the copy is isolated or immutable
Fire, theft, water damage	No	No	Yes, if it is on another site

The ANSSI, France’s national cybersecurity agency, recommends the “3-2-1” rule: three separate copies of the data, two backups on different media, one of them offline. Cybermalveillance.gouv.fr, the French government’s cybercrime assistance platform, also advises keeping a copy in a separate physical location and disconnecting the backup media after use.

4. Afterwards

Reinstate an external backup on the day the NAS goes back into service. Check the overnight alert. If the NAS was the only copy for the workstations (“we save to the NAS, so it’s backed up”), the scope was wrong: a NAS is a source, not a backup. See How to back up a NAS? and Why make an off-site backup?.

At WeDoBack

NAS devices are among the sources WeDoBack includes in its off-site backup: data is encrypted on the machine before it is sent, with a key held by the customer, then stored on servers dedicated to backup, separate from production. Restoration covers the copied data, to a sound location; it does not repair the RAID. If the NAS hosted the company’s only file server and downtime is unacceptable, the critical content should live on a server covered by a DRP, not just on a NAS restored file by file. Support can be reached on +33 9 72 50 78 28, from 9:00 to 13:00 and from 14:00 to 17:30 (Paris time).

Call +33 9 72 50 78 28 Request a quote

Frequently asked questions

Isn’t RAID enough to protect the data on a NAS?

No. RAID lets you survive the failure of one disk, sometimes two. It does not protect against deletion, ransomware, controller failure, fire or theft: all the copies are in the same enclosure. The ANSSI, France’s national cybersecurity agency, recommends three copies, on two different media, one of them offline.

Are NAS snapshots a backup?

They let you quickly go back to a previous version of a file, as long as the NAS is working. NIST points out that if the source data becomes unavailable, the snapshots can no longer be used either. They complement an external backup; they do not replace it.

Should the disks be sent to a data recovery specialist?

Only if no clean external copy exists and the data is valuable. In that case, shut the NAS down properly, number the disks in their original order and do not attempt anything else. Every rebuild attempt reduces the chances of recovery.

Sources

Documents consulted in October 2026.

Information system backup – The fundamentals (ANSSI-BP-100, v1.1, 27 November 2025, in French) — ANSSI
SP 800-209, Security Guidelines for Storage Infrastructure (October 2020) — NIST
Why and how to manage your backups properly (in French) — Cybermalveillance.gouv.fr
Ransomware: what to do if your organisation falls victim to an attack? (in French) — Cybermalveillance.gouv.fr
DRP offer (Disaster Recovery Plan) — WeDoBack

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