SOLVEDWell... i just post for other people that might have the same problem, ...
It seemed that when I tried to install the 1TB with the old of 500GB, the DNS started some kind of filesystem in the old disk, therefor, I couldn't see nothing at first, but when I stack the both of them, the bad one switched to the RAID partition, and showed it's content. But there was files that were corrupted (maybe because of the new partition?). Thats because Ubuntu couldn't do 'stat' to some of the files.
I putted the drive in Windows, and the same happend... "corrupted file". So I finally decided to try with the good disk (the one I took out first), and it seems to be OK. I'm actually with my other PC running Ubuntu Live CD, mounted the good disk, and copying to the new raid.
So, what have we learned today? xD Before doing anything crazy like sticking a new and bigger disk into the nas trying to autobuild the RAID, ask in the forum, seek on the internet, and use common sense with your important backup data