Ok that wouldn't be a big deal with the log files. For the program data I think there are some work arounds. I could implement unionfs with 2 partitions, one with a working state and the other as working dir. Then every x minutes I sync the files from the working dir to the working state. These writes are to an temp file, that are renamed after the write, to prevent corrupting the working state files.

Thanks for the great tutorial. Works great! If I would make a third partition on the SD card, and put the logs there and a fourth partition for the program data, would this still prevent my raspberry pi from not booting? The system files and programs would be read only. If not, would using an usb stick for the logs and program data be better?