Thanks. On the internet in NAS related forums and youtube, people like to recommend others to use RAID 5. Of course, we don't know their background. Could be somebody who heard form others and just made the same recommendation. That is why I asked in this well established site.
OK, so that would be some context on where you heard this.
With a 4 bay NAS box, a RAID 5,
maybe.
It provides physical drive redundancy, in the face of a single drive fail.
And only to keep the data up and accessible, until such time as you can take it offline to swap the dead drive and rebuild the array.
RAID is not a backup. That can't be stated enough times.
Your data ALSO needs a real backup, apart from and alongside the RAID.
When I first got my QNAP, I set it up as a RAID 5. 4x 3TB drives. Later, upgraded to 4x 4TB.
Before long though, I undid the RAID in favor of individual drives.
And further, once we get into larger drives and data consumption, RAID 5 becomes problematic.
When I switched from 4x 3TB to 4x 4TB, I did it one by one, just to see how the QNAP handled that.
There was about 6TB actual data space.
Swapping in the new 4TB drives, one by one, required about 8 hours each time to rebuild the array. So the whole thing took several days.