If I enable SMART monitoring for a disk under Disks|Management|Disk|Edit ("Activate S.M.A.R.T. monitoring for this device") and then navigate to Disks|Management|S.M.A.R.T. and enable that, save & restart then I get "Error: The changes could not be applied (error code 1)." in the web interface and the following entries in syslog:
root: Failed to start service smartd
root: /etc/rc.d/smartd: WARNING: failed to start smartd
smartd: Unable to register device /dev/ada0 (no Directive -d removable). Exiting.
smartd: Unable to register ATA device /dev/ada0 at line 1 of file /var/etc/smartd.conf
If I manually use smartclt on the disks in question it works fine - I can see the SMART data, run tests, print the results etc.