[jggimi]

In a default installation, "/mnt" is an empty directory in the root filesystem "/". Its purpose is to be a mount point for removable media or other temporarily accessed filesystems, as described in the hier(8) man page.

In your environment, you appear to have used this directory for other purposes, since you have a "/mnt/home/..." whereas the default filesystem for user directories is "/home".

The root filesystem is designed to hold the second-stage bootloader (/boot), kernels (/bsd* files), configuration files (/etc), device nodes (/dev), a mount point used for root filesystem backup (/altroot), static binary programs (/bin, /sbin), and mount points to all the other filesystems. The automatic allocation, if used, varies depending on architecture and the size of the physical drive. On large drives, the size of the root filesystem will typically be limited to 1GB, as it is in your configuration. See the AUTOMATIC DISK ALLOCATION section in disklabel(8) for details.

Without seeing your complete df(1) output, I will be unable to provide you with any recommendations.