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I’m wondering if I have a faulty/weird USB hub.

Whenever my external WD hard drive is connected to this cheap USB hub I own, which happens to have its own power supply, the hard drive will keep spinning on a low speed. The USB hub isn’t even connected to my computer.

The mouse that I have connected to the hub has the same behavior, where it will stay lit no matter if the hub is connected to the computer or not.

Is this the intended behavior of a USB hub? It seems like it unnecessarily keeps the hard drive spinning, potentially reducing its life span.

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Cheap USB hubs don't have intelligent power supply switches on downstream ports. Because of that, when on self-power, the VBUS power is always ON when you plug its AC-DC power adapter into wall. Unfortunately, this is a legal (from USB standpoint) hub configuration. Therefore, if you have a USB device plugged in, it will get VBUS and will power-up even if the hub is not connected to PC host. Then a device will try to connect.

However, if there is no USB communication, a good USB device should fall into power sleep mode (SUSPEND), and reduce its power consumption to 500 uA from VBUS (micro-Amps!). If a device doesn't do this, it is a broken, bad implementation, and it can't be USB-IF certified. So, if your external drive keeps spinning, it is broken, not the hub.

A good USB mouse should do the same, fall asleep in few moments after connect, and turn off all lights.

  • I don't recall there being a provision in the USB standard requiring devices to auto suspend in the absence of communication. Got a reference? – psusi Mar 5 '18 at 0:11
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    @psusi, this is by definition. Explicitly, p.150 of USB2.0 specs, "Anytime a device observes no bus activity, it must obey the rules of going into suspend (see Section 7.1.7.6).". – Ale..chenski Mar 5 '18 at 0:31
  • Thank you for your response. I went ahead and purchased a more modern and more expensive USB hub, and while the external HD seems to go to rest when I pull the plug from the computer, the mouse still has its lights turned on. This only happens after the hub has been connected to the computer. Can this behavior stem from how macOS handles USB, or from the mouse itself? – Simon Mar 5 '18 at 20:42
  • Never mind the external HD, it now acts the same problematic way as previously. – Simon Mar 5 '18 at 20:57
  • If you have the hub connected, and PC is soft-down, even a good hub will maintain VBUS power until it gets disconnected or receives USB reset. So the problem of no-suspend is on drive side. Try to disable power management on the hub, it might help to behave differently. – Ale..chenski Mar 5 '18 at 21:05

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