xenic wrote:Actually, I tested the USB MassStorage "Dismount" command and it doesn't do anything on my system.
That's strange, maybe something on your system is holding a lock on whatever drive you're testing with because on my system it removes the drive from the device list. With some further testing I've found that the Dismount function of the GUI does exactly the same thing as the Dismount DOS command: it simply calls dos.library DismountDevice() with the relevant device. This also means the same limitation exists there - once a device is dismounted, disconnecting and reconnecting the device won't make the volume show up again without manually mounting it. So the mass storage GUI isn't a good reference for simple "eject" functionality after all.
Slightly worrying perhaps, is that while the USB drive is still attached, the Mount function of the GUI can me used to remount the drive as expected, but if the drive is removed and then reconnected, it shows up as dismounted in the GUI, but clicking on Mount crashes my entire system. So, once dismounted, there's no apparent way to use a particular device again without rebooting.