It is really weird that volume encryption is not available. I have been trying to found it on the past days, since I turned a DNS-320L on for the first time, without success, even though this feature is explicitly described in the NAS manual! BTW, in the manual they have used firmware version 1.08 to take the screenshots. I tried with the original firmware on my NAS (1.03), and with 1.08, 1.09, and 1.10 and none of them provide this feature! it is really a shame what DLink is doing with this NAS.
Anyway, to the benefit of others, i want to provide a hack in order to activate this feature.
*** WARNING ***
I DO NOT GUARANTEE THIS WILL WORK! THIS CAN DAMAGE YOUR NAS, YOUR DISKS, AND YOUR DATA. USE IT WITH NOT WARRANTY!
THIS WILL PROBABLY VOID YOUR WARRANTY!
You can log into the NAS through SSH (this feature at least is available in recent firmwares). After logged in, I got an error saying that no homedir was defined for the admin user. Hence, I created one:
mkdir /home/admin
Then I logged off and logged in again through SSH. After that, copy the following file to your homedir:
cp /usr/local/modules/web/pages/function/define.js /home/admin/
Edit this file with vi and change the value of the VE_FUNCTION variable to 1.
Find the lighttpd process:
ps axuf | grep lighttpd
Kill it:
kill <pid>
Restart lighttpd:
/usr/sbin/lighttpd -D -m /usr/lighty_lib -f /etc/lighttpd/lighttpd.conf
You should be good now to log in in the Webu GUI and find the volume encryption options.
Unfortunately the configuration is lost every time the NAS is restarted. There is probably a way to edit the firmware image to persist this variable value change there, but I didn't try that. However, once the disk is encrypted, it will get mount correctly after a restart, even though you will not be able to see the volume encryption configuration in the Web GUI as it will be deactivated after the restart.
Another big warning: The disks are so painful slow with this option enabled that I think now I understand why DLink deactivated it. It seems to be really useless (probably due to the low profile embedded processor and/or very old linux they are using in DSN-320L).