I have checked in the current Buffalo manual and I now understand what the Auto switch is for
Quote from the manual
AUTO: When the switch is in the AUTO position, the LinkStation automatically turns off when all computers on the network with NAS Navigator2 turn off. If any computer on the network is powered on, the LinkStation automatically powers on as well.
ON: The LinkStation stays on, even when all computers are off.
OFF: Turns the LinkStation off.
The 'auto' is designed to turn on the NAS when a PC is turned on (just as long as it has the 'Navigator' software installed), and then turn off, when the the last PC on the network is turned off
It is using WOL to turn the NAS on when you turn on a PC
Once the NAS is on, it is not using WOL then, it's just sending it a signal to tell the NAS that the PC is still on, so that it doesn't turn itself off
From what I can see from the manual, there is no other 'hibernation' feature, unless it is not referred to in the manual
From several forums, it seems that the Buffalo does not support hard drive spin down, so as you said, setting the switch to On would mean the NAS stays on all the time, and if it is set to Auto and the PC is not accessing the NAS, the drives will still not spin down - this I think is a bit of a boob on Buffalo's part, as the whole point of a NAS is low power consumption, but the Buffalo is running at full power all the time it's turned on
All other NAS's I have come across have another 'hibernation' mode
This kicks in when a PC etc hasn't accessed the NAS for a specified period of time, and it allows the NAS to go in to a 'soft' hibernation (hard drives spin down to save power, but the NAS is still on), and to bring the NAS back awake, you just need to access a shared folder
Mine is set to hibernate every ten minutes giving me the following power consumption figures
1. NAS in use = 55 watts - instant access
2. 10 minute hibernation = 20 watts - take a few seconds to awake
3. Powered down for WOL = 1 watt - takes a couple of minutes to boot up
4. Completely powered down = 0 watts - takes a couple of minutes to boot up
Unless someone on this forum can replicate what you Navigator software does on the Humax to stop the NAS from shutting down, you may be out of luck