I got a little confused after I had read advices on https://wiki.archlinux.org/index.php/Partitioning and on https://help.ubuntu.com/12.04/installation-guide/powerpc/directory-tree.html. Why is there such a big difference between the sizes of the partitions? E.g., about / partition.
Typically 150–250MB is needed for the root partition.
15-20 GB should be sufficient for most users with modern hard disks.