The thing is, I already did the upgrade from stretch to buster on a rpi2 without any errors. And the rpi2's /boot drive is now 95% full.

So I guess the error with the rpi1 must be related to something else.

Okay, and what is your solution? Linux raspberrypi 4.19.57-v7+ pi@raspberrypi:~ $ df -h Filesystem Size Used Avail Use% Mounted on /dev/root 15G 2.5G 12G 18% / devtmpfs 459M 0 459M 0% /dev tmpfs 464M 1.9M 462M 1% /dev/shm tmpfs 464M 30M 434M 7% /run tmpfs 5.0M 4.0K 5.0M 1% /run/lock tmpfs 464M 0 464...

Hi, when I do want to upgrade my rpi1, I get the messages: Get: 305 http://raspbian.raspberrypi.org/raspbian buster/main armhf libpython2.7 -dev armhf 2.7.16-2 [30.9 MB] Err http://raspbian.raspberrypi.org/raspbian buster/main armhf libpython2.7-dev armhf 2.7.16-2 Error writing to output file - writ...