Why is one-to-many USB device attachment possible?

karypid

Member
Mar 7, 2021
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I have 2 VMs in my Proxmox: one has GPU passthrough for my main Linux desktop. The other is a Windows VM which I use for work (accessing my employer). I generally remote-desktop from Linux into the Windows VM with Remmina (it works great because it's basically a "localhost" connection) during work hours.

My question has to do with USB devices: I have a USB webcam is normally attached Windows VM all the time (for Zoom calls). Over this weekend I moved it to my desktop for personal use, then back to the Windows VM for use at work on Monday.

Today I spent a lot of time rebooting the Windows VM because the webcam did not work. To my surprise, the issue turned out to be that I had not removed the webcam from my personal Linux VM! In other words, the same webcam was attached to two VMs at the same time.

I am certain that I did not get any warning from Proxmox when I did this. I would expect that attaching a device to a second VM would pop up some error dialog (at least when you start the VM while the other one is running).

So I am assuming there may be some valid use case for this? Is there some scenario where a USB device can be attached to two running VMs and be useful? (hence why proxmox allows it?)
 

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