Cannot mount backup device

Hi there,

This might be a basic thing, but I seem to be missing something.

I am using a RPi4. I am working with a thumb drive for the system and a USB-SSD for the user data (nextcloud). This all works well. My plan is to backup the whole thing via the built-in backup solution on an additional USB SSD. I can make a backup to the attached SSD without any problems.

But as soon as I plug the additional drive in, things get messy. The system seems to re-mount all devices with sda becoming sdc and so forth. This leaves me without the possibility to render a backup to the additional drive since all mounts get lost. I even have to unplug everything, reboot and re-mount the original two drives to get the system running again.

What am I doing wrong?
Thank you for any hint!

can you check dmegs for “under-voltage” messages? Sounds like it becomes power issues when you plug the stick in. Have you other disks attached? If yes, with dedicated power supply?

dmesg | grep voltage
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Yes, how do you power your external HDD/SSD? Especially on RPi4 it is important to use external PSU because USB ports of RPi4 are not designed to power larger devices.

Thanks!
Attached devices are a USB thumb drive and a USB NVME enclosure. No dedicated power supply. This setup is running well. A third drive causes the problems I described.

dmesg | grep voltage

returns nothing.

As said, RPI4 is not able to power larger HDD/SSD very well via USB ports. It’s highly recommended to use external PSU or active USB hub.

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I will try a powered hub, then. Thanks for pointing that out!