disk free for samba that can determine fs type and calculate accordingly.

dfree

#!/bin/bash
#Originally by stanislavs from post http://stanislavs.org/reporting-correct-space-usage-for-samba-shared-zfs-volumes/#comment-2443
#Used some updated code from github user umito / Peter on that site  to clean up the non zfs code.

if [[ `findmnt -n -o FSTYPE -T "$PWD" | grep -c zfs` > 0 ]]
 then
# echo "DEBUG: this is zfs"
 USED=$((`zfs get -o value -Hp used $PWD` / 1024)) > /dev/null
 AVAIL=$((`zfs get -o value -Hp available $PWD` / 1024)) > /dev/null
 TOTAL=$(($USED+$AVAIL)) > /dev/null
 echo $TOTAL $AVAIL
else
# echo "DEBUG: this is not zfs "
 df $PWD | tail -1 | awk '{print $2" "$4}'

fi

Thanks - works well for both my ZFS for Linux samba shares and non-ZFS shares under Ubuntu 18.04.