When using ZFS as the file system the "df" command is reporting the pool sizeand not file system sizes.

[fbfortune@mastodon.bsd.cafe]

When using ZFS as the file system the "df" command is reporting the pool size
and not file system sizes. It also does not know about descendent ZFS
datasets, snapshots, quotas, and reservations with their individual space usage.
Use the built-in "zfs list" command to get a better overview of space usage:

zfs list -o space

-- Benedict Reuschling <bcr@FreeBSD.org>