Thank you very much for your replay, Igor.
Could you please be more precise? I'm not a linux expert.
Two or three years ago I found an instruction, how to boot Armbian from lvm, that worked for me,
but with this problem I'm overwhelmed.
When I try to mount /dev/mmcblk0p1/boot I get an error.
What do I exactly have to do to run the system on the lvm as if it is running on the SD card?