I’d say it depends on your circumstances and your tolerance to the possibility of data loss. The general answer to the question is that without using some kind of redundancy, either mirrored disks or RAID, the failure of a single disk would mean you lose your data. This is true for each copy of your data that you have.
Why? If there are offsite backups that can be restored in an acceptable time frame, what’s still the point of RAID?
I’d say it depends on your circumstances and your tolerance to the possibility of data loss. The general answer to the question is that without using some kind of redundancy, either mirrored disks or RAID, the failure of a single disk would mean you lose your data. This is true for each copy of your data that you have.