Comment # 3 on bug 995782 from Stefan Hundhammer

This is intentional. There is a maximum size for the root partition that can be
set in a product's control.xml file. For example, this is the relevant section
of that file for SLES-12 SP2 (Leap 42.1 might be somewhat different, but
certainly similar):


    <partitioning>
        <try_separate_home config:type="boolean">true</try_separate_home>
        <limit_try_home>5GB</limit_try_home>
        <root_space_percent>40</root_space_percent>
        <root_base_size>3GB</root_base_size>
        <root_max_size>10GB</root_max_size>
        <proposal_lvm config:type="boolean">false</proposal_lvm>
        <vm_desired_size>15GB</vm_desired_size>
        <vm_home_max_size>25GB</vm_home_max_size>
        <btrfs_increase_percentage
config:type="integer">300</btrfs_increase_percentage>
        <!-- the default subvolume "@" was requested by product management -->
        <btrfs_default_subvolume>@</btrfs_default_subvolume>
    </partitioning>

Those parameters interact with each other, and some are treated differently for
example if the root file system is Btrfs (in this example there is a 300%
increase in that case to make room for Btrfs snapshots).

The general idea behind holding back free space in case of an LVM installation
is to have some spare disk space for additional LVM physical volumes that can
be used for additional LVM volume groups.

I am not the one to decide if this is a good or a bad idea, but that was
requested as a feature by product management a long time ago. And it's
configurable per product via this control.xml file.


Bottom line: This is the intended behaviour.