What risk are you worried about?
Having a DNS-323 in RAID 1 (redundant disk) mode gives you excellent protection against mechanical or electrical failure of either disk DUE TO RANDOM EVENTS. The chance is truly miniscule that one disk would fail, and the second follow would before you could obtain and install a replacement disk. Not a zero chance, but definitely you could claim some geek sympathy.
The chances are much higher that both disks and/or the DNS itself will fail if the unit falls off a shelf, your house burns down or is flooded, your power line is struck by lightning, or if there is a software error that nobody knows about (yet).
The chance is essentially 100% that you will lose data if you delete it inadvertently.
If you have data that you really, truly can't afford to lose, then you can't afford not to have one or more off-site backup copies, preferably on write-once media. Only you can make the call as to what qualifies.
Personally, I run my PC with a RAID-0 pair of disks, make frequent backups of critical data to my DNS-323 with a pair running in RAID-1, and sleep like a baby.