Why RAID Is Not a Backup

RAID exists to keep a machine running when a disk dies. That is a availability feature, not a data-protection feature, and the distinction matters the first time something goes wrong that isn't a dead disk.

What RAID actually protects against

A single drive failure in a redundant array. The array degrades, you replace the disk, the array rebuilds. Your work continues. That is genuinely useful and worth having.

What RAID does not protect against

Every one of these destroys or corrupts data on all disks at once:

• Accidental deletion — the delete is written to every disk in the array.
• Ransomware — encryption is written to every disk in the array.
• Theft — the array leaves the building intact.
• Fire, flood, or power surge — the whole chassis is affected.
• Controller or filesystem corruption — redundancy replicates the damage.

The practical rule

Treat RAID as uptime insurance and keep a separate, offsite, versioned copy for everything else. If your only copy of a file lives inside one physical box, you do not have a backup — you have a single point of failure with extra disks in it.