Hi,
I also needed a solution for this, but also for streaming hd video, and did some research a few months ago.
First, as others say, RAID is not a backup solution, so why get it...speed? What speed? Streaming flac can be done on a 5y old cellphone let alone any modern harddrive. Reduce downtime? Cmon, a hd breakdown every second year tops and a few minutes of downtime worst case is NOT worth investing time and money in (while swapping the hd).
So skip that bull, sounds nice but it's only good for uptime and/or speed which is not a problem in this case.
Then we have the network-attached part. In my case I also needed a decent router for fast wifi (if wifi is not needed for you, there probably are slightly cheaper solutions), and while many routers and network storage gadgets boast different speeds, to really reliably be able to saturate a 100mbit network through wifi I'd say anything that doesn't use the "ac" wifi standard won't do it (unless maybe in the same room), but the client machine would need an "ac" capable wifi as well (there are usb-sticks...). There are plenty of routers with usb to attach drives of different sorts, but not many have the processing horsepower to get good throughput and also usb3. But what I found was the then rather new ASUS 68u router that has this, and I can reliably get 30mb/s (not mbit, I get about 240 mbit/s) through wifi, a couple of rooms away, which is more than some "real" NAS:es provide. I have connected a cheap (~$50) five-hd-slot usb3-hardrive box to it's usb3 port (which supports raid but I don't use it, but it also sleeps the disks after 15 min of no use), but so far I've "only" populated it with 3x3TB WD Red series harddrives.
Works like a charm both for streaming HD music and supplying my mobile devices with great bandwidth and full speed access to my 100mbit internet connection.
As for backup: For really important stuff, buy a large but slow (to reduce price) HD and store offsite except when backing up (othwerwise a fire for example would wipe both the data and backups), or for more convenience, for example google has lowered the price for online storage substantially if not that much data ($9.99/TB per month). For the rest I'm lazy and simply map the network drives to my windows machine (like Z:\ so it looks like a local hd to my computer) and run a simple one-line "robocopy" script between them now and then (but it could easily be scheduled or even probably run on the router not needing a computer to run the backups, if logging to the router with ssg and using similar tools in the routers under-the-hood linux OS to set up the script and schedule it), using one of the drives as "master" and the other one as backup:
robocopy Y:\Music Z:\Audio\Music /MIR /FFT /LOG:MusicBackup.log /TEE
(The script simply copies anything changed in "Y:\Music" to "Z:\Audio\Music" and removes files removed from y, and creates a logfile)
Cheap (relative to a NAS of similar performance), great wifi speeds all over, safe, and a supberb router for other purposes if you need those (guest networks, lots of firewall/portforwarding and similar functionality etc), really works well for me.
Good luck!
