I did similar way to upgrade my QUAD 2T to 6T.
However, after the four disks were swapped, I can't access the box anymore after 36 hr of RAID 5 format and 24 hr or data move.
Now the Linkstation Quad box flashing with 6 time red power light (which means hard disk problem).
If I put the original 4 500G disks back in, the NAS box functions with no problem.
B.T.W. I have the firmware updated from 1.05 to 1.10, then to 1.11 and makes no difference.
I know the 1.5 TB disks are working disk, I think the NAS' OS wrote something to the disks to indicate they are non Buffalo replace disks and refuses to work from there.
Any suggestion to have it fix so that I can copy the data I move into the RAID-5 disks back ?