Hello,
I would like to use the sd card reader from my raspberry pi to backup data from another sd card I have.
Is that technically possible or does the SD card to be mounted the whole time?
Thanks in advance,
Benjamin
You really shouldn’t be removing the SD card from a running system.
You can try looking into rsync to backup data between running devices across the network though.
The intention was to use the raspberry pi as sd card reader.
I thought having osmc installed on usb pen gives me the chance to remove sd card when the system booted up.
Sorry, this screwdriver was not intended to drive a nail… 
Well the boot parition is mounted, so you first would need to unmount it before you unplug the card.
So some how it should be possible but connecting a USB SD card reader might be a much easier approach.
So you can confirm that this should work after unmounting the boot partition? 
Well it technically works but as soon as any process tries to access it (e.g. MyOSMC) then you will have a problem. So for a short period to just do what you want you most likely will get away.