And this serves to demonstrate a few points:
First: If it's your only copy, it's NOT a backup.
No matter how trouble-free your storage has been historically, if you don't have a backup, you will lose data someday.
Back-up everything that's worth keeping.
RAID isn't a backup, it's a form of redundancy that still has its limitations, RAID corruption for example.
An easy backup solution with Buffalo NAS's is to plug in a USB drive and use it as a backup target. This is typically a fairly inexpensive solution. It's still "on site", but at least it ensures that there will be two copies of everything.
A better solution is using another Buffalo NAS as a backup target. That way, you can move the second device to some other location on the same LAN. For example, you could run network cabling through the attic to your garage at the opposite side of the house from your NAS. That's a slightly better approach to fire-proofing your backups.
Another solution is to make another Buffalo NAS a backup target, through a VPN tunnel. I haven't tried this, but it should allow you to target a NAS that you set up elsewhere; a friend's home, your office, etc.