Many problems with write / read problems to the 500GB WD disk I installed in this unit. These were much improved but not resolved by a firmware update. The DNS313 also has a poor operator interface which can loose settings (such as all user details). The ftp server stopped working and only came back after a factory re-set. In addition the security model implemented on this device is crude and almost useless.
The last thing you need in a storage device is unreliability and for this reason I suggest you avoid the DNS313.