RAID guards against one kind of hardware failure. There’s lots of failure modes that it doesn’t guard against.
- File corruption
- Human error (deleting files by mistake)
- Catastrophic damage (someone dumps water onto the server)
- Viruses and other malware
- Software bugs that wipe out data
- Hardware problems that wipe out data or cause hardware damage (controller malfunctions, firmware bugs, voltage spikes, …)
and more.