If you have a problem with the files transfer like speed 1-2MB per second.
You have to enable ssh, login with putty to the nas and go to /etc/exports

You will see a table with your shares and inside sync
replace sync with async and reboot the nas!
zyxel nas 326 settings.png
zyxel nas 326 settings.png (6.81 KiB) Viewed 208 times
If you need even more speed add noatime as well.

Congrats!