root@dali:~# cat backup.sh 
#!/bin/bash

i=0
dataset=data/postgresql
wal=data/postgresql/wal
while true; do
        id=$(printf "%03d%s\n" $i)
        echo Switch pg in backup mode
        sudo -i -u postgres psql -c "select pg_start_backup('$id')"
        echo Creating postgresql snapshot
        zfs snapshot ${dataset}@$id
        echo Removing backup mode
        sudo -i -u postgres psql -c "select pg_stop_backup()"
        echo Creating wal snapshot
        zfs snapshot ${wal}@$id
        echo Sleep
        i=$(( $i + 1 ))
        sleep 15
done