"It is on the NAS, and the NAS has RAID." That sentence describes protection against exactly one failure mode — a disk dying — and none of the others.
RAID is availability. Backup is recoverability. Conflating them is the most common reason people lose data they believed was safe.
What changed in 2026
- Ransomware kept targeting network storage. Attacks specifically sought and encrypted network shares and connected backups.
- Immutable snapshot support spread. More NAS platforms offered snapshots that cannot be deleted before an expiry.
- Cloud backup pricing stabilised. Off-site storage remained affordable for typical home volumes.
- Larger drives lengthened rebuild times. Higher capacities meant longer, riskier RAID rebuilds.
What RAID does and does not do
| Threat |
RAID |
Backup |
| Disk fails |
Protects |
Protects |
| Accidental deletion |
No — replicates instantly |
Protects |
| Ransomware |
No — encrypts the array |
Protects, if isolated |
| File corruption |
No — corrupts on all disks |
Protects |
| NAS hardware failure |
No |
Protects |
| Fire, flood, theft |
No |
Protects, if off-site |
| Bad software overwriting files |
No |
Protects |
Only the first row is a RAID job. Every other row requires a separate copy that is not the live one.
The rebuild risk is worth noting: replacing a failed disk means reading every remaining disk completely, which is exactly when a second failure is most likely. With large drives that read takes a long time, and a second failure during it loses the array. That is a reason to have backups, not a reason to avoid RAID.
The 3-2-1 rule
Three copies of the data, on two different media types, with one off-site.
Three copies. The live data plus two backups. Two copies means one failure away from one copy.
Two media. Not two disks in the same array, and ideally not identical drives bought together — drives from the same batch can fail together.
One off-site. This is what covers fire, flood, and theft, and it is the one people skip. Cloud backup or a drive kept elsewhere both work.
For a NAS specifically: the array is copy one. A local backup — an external drive or a second NAS — is copy two. Cloud or a rotated off-site drive is copy three.
The off-site copy should be write-limited from the NAS side where possible. A backup the NAS can freely overwrite is a backup ransomware on the NAS can destroy.
Snapshots and immutability
Snapshots are point-in-time views of the filesystem, cheap to take and fast to restore from. They are excellent against deletion and against ransomware — provided they cannot be deleted.
That is the crucial qualifier. Ransomware that gains administrative access will delete snapshots before encrypting, so snapshots only defend if the platform supports immutable snapshots that cannot be removed until they expire, regardless of credentials.
Practically: enable frequent snapshots with a retention schedule, make them immutable where supported, and keep administrative credentials separate from everyday ones.
Snapshots are not a substitute for off-site copies. They live on the same hardware, so they do nothing for fire, theft, or controller failure.
For the personal-document version of the same problem, document vault covers what to protect first.
Test restores
The step everyone skips, and the one that determines whether the strategy works.
A backup that has never been restored is a hypothesis. Common failure modes discovered only at restore time: the job silently stopped months ago, the encryption key is on the machine being restored, the backup contains a folder nobody needed, or the restore takes days.
Test quarterly. Restore a handful of files to a different location and verify the contents. Occasionally test a full restore to understand how long it takes.
Check that alerts work by deliberately failing a job. A monitoring system that has never fired is also a hypothesis.
Store credentials and keys separately from the system being backed up.
Common mistakes
- Treating RAID as backup. Different problem entirely.
- Sync as backup. Deletion propagates.
- Backup drive permanently connected and writable. Ransomware reaches it.
- Snapshots that are not immutable. Deleted before encryption.
- No off-site copy. Fire and theft unaddressed.
- Never testing restores. Failure discovered when it matters.
- Encryption keys stored only on the source. Unrecoverable.
FAQ
Is cloud sync a backup?
No. Sync replicates changes, including deletions and encryption. Versioning helps and has limits — retention windows are frequently shorter than the time it takes to notice a problem.
How many disks should a NAS have?
Enough redundancy that a single failure does not lose data, plus backups regardless. More disks in the array is not a substitute for the second copy.
What about backing up the NAS to another NAS?
Reasonable as copy two, particularly with a pull-based configuration so the source cannot write to the destination. It still needs to be off-site to count as copy three.
How often should backups run?
Frequently enough that losing the interval is acceptable. Daily suits most home use; more often for actively changing work.
Where to go next
For power protection on the NAS itself, read UPS sizing. For personal document protection, document vault, and for the flash storage side, USB flash endurance.