USB device won’t mount? Is your hub powered or not?

Here’s something I just discovered. Maybe it’s “old news” or maybe it’s “just me” but FWIW

Based on my own experience, there is a subtle difference between powered and unpowered USB 3.0 hubs: sometimes a powered-hub device is not recognized.

Specifically I have an external USB 3 trayless enclosure that I use for swapping in/out bare drives for backups and so on.

My process is, with the enclosure powered off, I insert a drive. Power it on; wait for the drive to appear on the desktop; use it; eject it; and power off the enclosure before removing the drive. Wash, rinse, repeat.

The enclosure was been plugged into a powered USB 3 hub, and that “mostly” worked. But many times, I’d insert a drive and power up the enclosure and the disk never appeared on the desktop. Unplugging and replugging the hub caused things to work again.

I noticed something similar with USB flash-drives (sticks) as well, when used with powered hubs, so it’s not just this one enclosure.

A few days ago, I switched to an UN-powered hub… and everything “just works” now.

I suspect that a powered hub may present a unchanging signal of some kind to the device, and that in turn prevents a new device from being recognized. Perhaps the continual power makes it difficult for the system to recognize that the device has been -removed- instead. I dunno, but I do strongly suspect that something like that is going on.

Devices that do -not- have their own power switch/supply seem to have no problems at all with a powered hub.

As usual: YMMV.

Tracy
www.valleau.art

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