Raspberry Pi 4 Model B on-board WiFi drops when USB 3.0 flash drive is connected. When the flash drive is disconnected, WiFi starts working again.

I'm running a Raspberry Pi 4 Model B Rev 1.2 as a bridge/router between my phone's hotspot and my LAN. I'm powering the Pi using the official USB-C power supply. I want to be able to connect a USB 3.0 flash drive which stores media and then run Plex on the Pi to share the media on my LAN.

First I setup the router side of things so that I had internet connectivity on my LAN. This works absolutely find, 24/7.

I then turned to setting up storage. It's my intention to use a large (128GB) USB flash drive (this one). I connected the flash drive to one of the USB 3.0 ports on the Pi. I was able to log in to the Pi, then format the flash drive and mount it before I realised that I was no longer able to connect to the internet on my LAN or from the Pi. It's as if the Pi had dropped it's connection to my phone's hotspot.

As the connection of the flash drive was the last thing I did, I disconnected it and I noticed that the link/activity LEDs on the ethernet port on the Pi both went off for a few seconds, then came back on. I went back to my PC (where my SSH connection to the Pi was still running) and I could see that I was able to connect to the internet again. The Pi itself doesn't seem to power down or anything when I saw the ethernet port lights go out and then come back on; it just seems to be the ethernet port that turns off and then back on again when the flash drive is disconnected.

I wondered if there was some issue with the top-most USB 3.0 port, so I repeated the steps, but connected the flash drive to the bottom-most USB 3.0 port. I got the same behaviour.

I can recreate the problem with two other different flash drives (16GB and 32GB) which are both the same model as the 128GB one, but are very different ages.

I reconnected the flash drive and the WiFi connection between the Pi and my phone dropped and I thought I'd try to dig into the problem to find out what's happening, however I was unable to find any logs or anything which indicated there was a problem, apart from the fact that there was no internet connectivity.

When I run ifup wlan0 I see it sit there waiting for a DHCP lease from my phone's hotspot -- which is normal -- but then it never gets a lease and times out. It would appear that there's no connectivity over the WiFi connection on the Pi when the USB flash drive is connected.

I don't get the issue when I connect a USB 3.0 flash drive to the USB 2.0 ports on the Pi, so it does seem to be isolated to the USB 3.0 ports. One think to note is that when I connected a flash drive to a USB 2.0 port, I saw the ether port's LEDs go out and then come back on. This is different to when I use a USB 3.0 port. when I connect a flash drive to USB 2.0, the ethernet port's LEDs go out then come back on, but on removing the flash drive from said port, I don't see the LEDs turn off. However, when inserting the same flash drive to the USB 3.0 port, I see the inverse: the LEDs remain on when I connect the flash drive to a USB 3.0 port, but then go out and come back on when I remove it (as explained above). Really weird.

Any ideas what could be causing this, or what I can do to troubleshoot further?

  • if you have a USB hub, then try using that between the RPi and the flash drive, just to see what happens
    – jsotola
    Nov 17 '21 at 16:56
  • @jsotola Sadly, I don't own a USB hub.
    – JoeNyland
    Nov 18 '21 at 8:21

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