Theoretically though, since it's RAID1, both drives should have identical information.
As such, I know if I make the RAID using RST within Windows, there's an option to "keep data from x drive". Perhaps that'll work, but I guess I should really copy everything elsewhere first.
I do have a RAID10 on a LSI card of 1.8TB which might be sufficient, along with another 1TB or so on my desktop. It's just going to be a time consuming operation...
In my ideal world, I'd just plug the drives in and it would "remember" that it's RAID1 and be on my way

I'm guessing it won't work like that though.