RAID is not a backup.
It really is as simple as that, and it is helpful to remind people so they do not suffer the harms likely to result from mistakenly believing that RAID is a backup.
It really is as simple as that, and it is helpful to remind people so they do not suffer the harms likely to result from mistakenly believing that RAID is a backup.
There is backup because a disks are unreliable and fail randomly. RAID is designed to solve this.
There is backup because you accidentally deleted a file. There is backup because ransomware encrypted your files. RAID with snapshots solve these (arguably better than most other backup systems).
There is backup because your main computers (phone) might break. NAS systems are a good place to backup these.
There is backup because your house burned down [or otherwise is destroyed]. This is the only one that RAID doesn't solve. (even then you can do offsite NAS)
What risks do you need to mitigate? Once you have that list you can decide what you mitigations to apply. RAID is a very useful piece of this and so saying RAID is not backup is not helpful and may harm people from making useful backups because they let the search for perfection delay them.