Hi,
I don't think RAID 1 is really a problem because you can take one of the disks, attach it to a Linux computer (e.g. in an external case and using Ubuntu from a USB stick) and then mount the corresponding partition. I worried about that RAID stuff, too and tested it. The file system could be accessed without problems.
In addition to having RAID 1 I do a regular backup to a USB disk attached to the DNS-320 using rsync.
Just try it ;-)
Oli