I have a small linux system (kind of like a raspberry pi, but alot smaller and cheaper) that I want to use to back up files by rSync on a roughly-monthly basis. My problem is that the board doesn't have a Wake-on-lan capable chipset... I don't really want to generate excess heat and use lots of energy if the intended usage is only a handful of hours every year overall... I've heard one can use a NIC (relatively cheap?) to interface with the CAT5 cable before it hits the board to do something similar? I'm open to alternatives as well, as long as I don't need to manually go and power up the device every month. Any resources and or ideas would be great! I really don't want to change boards as this one is very inexpensive and is pretty good quality for what I need.

  • \$\begingroup\$ What if you were to add a small WiFi SoC (ESP8266 example) that would be always powered on, and then you could connect to that to trigger a system boot. Effectively hacking together the same effect as WoL, but using a separate communication channel. \$\endgroup\$ – uint128_t Dec 6 '16 at 22:52
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    \$\begingroup\$ @uint128_t then you'd have to power the WiFi thingy continously. I'm not sure you're gaining anything in the long run, because either you add yet another power supply, or you power it off the same supply that you could use to power the single board computer in a low-consumption mode. \$\endgroup\$ – Marcus Müller Dec 6 '16 at 22:56
  • \$\begingroup\$ @MarcusMüller Yes, but it would at least be less power than running the box itself continuously. It's not a great solution though. Honestly, I think the best solution for OP is to switch to a system that supports WoL out of the box. \$\endgroup\$ – uint128_t Dec 7 '16 at 0:16
  • \$\begingroup\$ @uint128_t I am really not sure about the "it's better than running the system continously"; imagine running continuously meant mostly idling its CPU, so that it's in a power-saving pseudosleep state, and mostly having all the peripherals turned off, only turning on the ethernet controller once every couple seconds, just to watch out for a few specific packets. \$\endgroup\$ – Marcus Müller Dec 7 '16 at 0:18

Most NICs will need configuration through a PCIe or PCI host before they will be wakeable-on-LAN, so I have some practical doubts on your approach.

Also, Wake-On-LAN isn't based on unicorn magic, but electricity. It works by letting the ethernet controller in the NIC run continuously but not do much stuff, just listen for a packet containing a certain byte sequence. Hence, instead of powering your probably low-energy optimized device, you're trying to run PC hardware which will itself need a power supply. In a PC, there's a few supply chains running even when the PC is off, exactly to support this kind of operation. By the way, WoL also means that your ethernet switch needs to be forwarding broadcast packets to the (sleeping) computer, which means the ethernet port can't be switched off – which wastes power again. The question whether letting your single board computer run continously is so much worse than letting a ready-to-wake-up circuitry run can only be confirmed by power consumption measurements of your system.

I'd strongly suggest looking into your board (which you sadly don't specify) and its low-power modes. How long does it take to go from suspend-to-ram to running? How much power does it consume in run and in sleep mode? Is it feasible to wake it up for a split second every 20s, send a broadcast packet that it's up, wait a couple milliseconds for a reply packet, and if nothing signals that there's reason to stay awake, goes back to sleep. That way, the computer only needs a small fraction of its run-mode power, still is available in acceptable time when you need it, and also, the network switch can power down its ethernet port – which might actually compete with your computers "not doing much at all" power consumption!

  • \$\begingroup\$ This board is more or less it. nz3o.wordpress.com/2011/12/18/… I can run suspend or sleep or hibernate from a debian hack, but haven't tried as I always just shutdown (I have no need for the features of sleep as I am only going to run rsync for backup once a month). I only really need an ethernet and a SATA port, which is why I chose this board. I thought it natively hat WoL... I was planning on using WoL to cut the 16V power from the PSU to the MOBO, while still allowing power to the NIC or something around those lines... \$\endgroup\$ – Jordan Austin Dec 6 '16 at 22:44
  • \$\begingroup\$ WoL needs a powered NIC. you can never power off all components of your system \$\endgroup\$ – Marcus Müller Dec 6 '16 at 22:54
  • \$\begingroup\$ As I said, I'd cut power to the MOBO without cutting power to the NIC. NIC could run a FET/diode or a relay. The power supply can run regardless? Alternatively I could just cut power to the HDD so I'm not running that 24/7, if I could find a way to make it always mount to the same point and if I could find a way to run a FET/diode off a USB data pin (don't even know if you can run boolean logic through a USB manually). I'm open to an alternative board if it's cheap and doesn't have a crapton of extra un-needed featured. This board doesn't even have the ability to run UIs, which is perfect. \$\endgroup\$ – Jordan Austin Dec 6 '16 at 23:11
  • \$\begingroup\$ and by letting your power supply run continuedly to supply 50mA to the NIC instead of 100mA to your CPU you win what, considering your PSU's efficiency? Linux puts your disk to sleep, anyway, your MOSFET shouldn't do anything (or at least not much). And again, as said, WoL doesn't work using awesome unicorn magic. For the board to be able to be woken up, it needs to be partly powered, so no complete cutting it from power, anyway! \$\endgroup\$ – Marcus Müller Dec 6 '16 at 23:13
  • \$\begingroup\$ I'd like to encourage you to do a power measurement on the wall side of your boards supply when its operating without doing anything, when having disabled its ethernet port, and when in an state from which you can wake it up. My suspicion is that you're chasing imaginary power savings. \$\endgroup\$ – Marcus Müller Dec 7 '16 at 14:08
