Ty said:
I'm not sure if a NAS is the same as what you are considering.
Yes, he is looking at a NAS (Network Attached Storage).
ERP:
I would skip it, and use an old computer.
Most consumer (read: cheap) NAS devices have no redundancy, and so I'd not trust them as any sort of file repository for anything that you don't want to lose.
The more expensive NAS you list (Terastation) does have redundant potential (depends on how you config it), but it is $1000 - if you have a decent old computer, you can get a decent SATA raid card and drives for less, and have much more flexibility - the cost is that you then must set up the device. Depends on your skillset as to whether or not its worth it, and it depends on how much money matters to you.
Personally, I use an "old" computer - Althlon XP 1700+ with 384mb of ram (which is way overkill, but heck, I had the chip to spare to replace the duron 600 that was in it up until a few months ago), with 5 160GB drives in RAID5. I can have a total of up to 8 drives with the raid controller I am using, as well as do online capacity expansion (add drives and space without going offline or losing any data) which I have done - I recently grew the array from 3 drives to 5 when I began to get short on space. It works great (I've test failed the array by yanking one drives cable - worked great, no hiccups, rebuilt fine), and gives me some confidence that the data I store on it is safer. Now I just need a cost effective way to back up the data....
Damn data security paranoia - I get it from work. RAID only protects from a HD failure. Remember kids, backup your stuff!