ReadyNas 3200 upgarde 1TB Hard drive to 2TB Hard drives

Well the problem with anything that's in raid is that no matter what size drive you use you're going to end up with only being able to use the amount of space on that drive that equals the smallest hard drive you've got in your array.

You can do Flex-Raid and add in drives all all different sizes and it will use all the available space possible, but the problem with that is there's no redundancy and each time you'd want to add a bigger drive, you'd have to delete the volume and then start over (which would be rather tedious.)

If you're planning on running mission critical stuff off of this Nas box then I'd recommend enterprise drives but if you're just using it as a file server or whatnot then I'd buy the cheapest 2TB drives I could get my hands on and throw them into an array and start out with 12 2TB drives. Me personally I just picked up a few seagate 8TB archive drives (spoiler alert, they aren't really meant for RAID but I've picked up all mine for $200 or less) and then add additional drives as I find them. So far I have 5 in a 6 bay unit.

You can also update your unit to readynas 6.0 (look up 6.0 legacy here on the forums and there should be a guide.) Software 6.0 has a much more robust set of features that are in my opinoin easier to use. It would install nicely on your unit. If I were you depending on what you're going to use the box for in the future I'd look at 3TB or 4TB drives to start off with and add as many as you want in the future. It's much easier to expand that way than having to back up all your data, wipe out your volume and then install new drives and a new volume.

And if you have no use for all 12 bays, let me know! I have a pro 6 (6 bay unit.) Perhaps I could buy that unit from you if you were interested (have always wanted a 12 bay unit!)