2015-06-11, 00:05
I haven't checked prices but when helped a friend setup an unRAID server a couple months ago we went with 4TB drives since they seemed to be the best combination of size and affordability at the time.
Whatever you do, sounds like you could get away with 1 drive for now. For example, if you bought a 6TB drive, set it up as the data drive, copy your 4TB of data to the data drive from your existing 6TB drive. Then install your 6TB drive and set it as parity. Then you can copy the data from the 1TB drive to the server and then install the 1TB drive as an additional data drive on your array. That would give you 7TB of parity protected space on the array plus the ability to add additional drives up to 6TB in size to the array.
Whatever you do, sounds like you could get away with 1 drive for now. For example, if you bought a 6TB drive, set it up as the data drive, copy your 4TB of data to the data drive from your existing 6TB drive. Then install your 6TB drive and set it as parity. Then you can copy the data from the 1TB drive to the server and then install the 1TB drive as an additional data drive on your array. That would give you 7TB of parity protected space on the array plus the ability to add additional drives up to 6TB in size to the array.