We have been buying these NASs to be used AS backups to our clients networks. We have the device setup in a LAN network and then install DirSync (http://www.archersoft.com) on their server. Every night at midnight, the DirSync software copies everything from the server, as well as every other windows PC on the network, to the DNS-321 under a "Backup" folder - each computer has it's own folder on the NAS. We use DirSync is because it has been the best backup/directory syncing software we found, and I tested at least 2 dozen of them myself. There are lots of free ones you can use, like Cobian Backup, that do the same thing, but not quite as well. The best 2 features about these types of softwares are (In my opinion)...
1) You can set it to only backup what has changed, so the first backup takes hours, but every backup after that could take minutes.
2) DirSync keeps Deleted Files for a configurable amount of time, as well as any number of different "versions" of backed up files. With a 1TB drive in the DNS-321, I set the software to keep Deleted Files for 30 days and up to 10 different versions of files. This means that if I have a file on my computer and it's backed up to the NAS, if I delete it from my computer, I have up to 30 days to go back and get it off of the NAS. And if I have files that change daily (like my Outlook .PST file), it will keep the last 10 different versions at all times. So if my Outlook file gets corrupted, I have up to 9 other versions to go back to.
Like I said, we use these NASs as the backup themselves, but the same thing applies to anyone using these to store data that wants a backup of the data. The backup has to be somewhere else, like another DNS-321, or a USB Drive attached to a PC on the network, or even another PC on the network itself. But if you install DirSync (or any other backup/syncing) programs on any PC on the network, you can schedule toe backup to run daily, weekly, or whenever you want.
I have a few clients that have 2 DNS-321's, each with a single 1TB drive in each one. I don't put 2 hard drives in them because 1TB is enough space for now, and mirroring doesn't help (for the cost) because these are a backup to data that is already on the computers anyway. But they each have 2 NASs that are configured identically, and they switch them out once a week. Some of them take one NAS home with them each week for an offsite backup, and some lock them in the office in fire-proof safe that is fire-proof for hours (not for a few minutes like cheap safes).
Anyway, if anyone has any questions, feel free to let me know.
Josh
PC Werks
http://www.mypcwerks.com