The difference is humongous!!! Archive drives are built for just that purpose... to archive and nothing else. They use a technology called SMR (shingled magnetic recording) where they write data in tracks that actually overlap each other. The problem is that if a single byte of the data needs to be changed, it'll have to take an entire section of the drive's data, read it and store it in it's RAM, erase it, then rewrite it all new again with the one new changed bit. They are intended only for something like incremental backups, wherein only new data is added and is only occasionally read. If you need to ever actually alter data, they perform at around 10-20% the speed of normal drives.
NAS drives on the other hand are pretty similar to regular desktop drives with just a few differences. For one, they are better able to handle the vibration caused by being in an enclosure next to several other drives. Also, they generally don't spin down completely during long periods of inactivity but rather go into a lower RPM mode to save power, yet can still access data within about a second from the first request.
If you're considering putting an archive drive in a NAS, please reconsider! That having been said, if you're only setting up a one or two drive NAS a regular desktop drive will usually suffice just fine. I've got pleanty of NAS's running up to 8 drives each and I generally just load them with regular desktop computer HGST drives. I've had yet to experience any issues from them.
From what you're describing, I'd recommend you just get three HGST desktop drives and do a RAID 5 of them. If you're adding a RAID controller that supports SAS drives, you can throw some nice enterprise grade drives in there and it'll really fly.
Hope this helps.
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