It appears that there is NO way to copy one Disk1 to Disk2 with good speed inside LS421DE... Hard to imagine why this was omitted in WEB interface of this NAS. If I need to upgrade one of disks to larger one, I need to copy data to some external storage and then back to NAS. I would not buy this NAS if was aware of that earlier :-(... If "performance matters" for Buffalo, why hours of time should be wasted during disk upgrade?