RAID is generally a good thing but don’t get complacent, follow the 3-2-1 method

To expand on that: Redundant drive setup and backups serve completely different purposes. The only overlap is in case of a single disk failure, where RAID (or similar) may save the data.

Redundancy is all about reducing downtime in case of single hardware failures. Backups not only protect you from data loss in case of multiple simultaneous failures, but also from accidental deletion. Failures that require restoration of data almost always involve downtime. In short: You always need backups (unless it’s strictly a local cache, and easily recreatable), but if you want high availability, redundancy may help.

3-2-1-rule for backups, in case you’re unfamiliar: 3 copies of important data, on 2 different media, with 1 off-site.