gistfile1.txt

jjulian at questor in /tmp/foo.mnt 
$ df -h .
Filesystem      Size  Used Avail Use% Mounted on
none             16G     0   16G   0% /tmp/foo.mnt

jjulian at questor in /tmp/foo.mnt 
$ truncate --size=5G fubar

jjulian at questor in /tmp/foo.mnt 
$ ls -l fubar
-rw-r--r-- 1 jjulian jjulian 5368709120 Mar 18 13:48 fubar

jjulian at questor in /tmp/foo.mnt 
$ df -h .
Filesystem      Size  Used Avail Use% Mounted on
none             16G     0   16G   0% /tmp/foo.mnt

jjulian at questor in /tmp/foo.mnt 
$ tar cvpf foo.tar fubar   
fubar

jjulian at questor in /tmp/foo.mnt 
$ ls -lh foo.tar
-rw-r--r-- 1 jjulian jjulian 5.1G Mar 18 13:49 foo.tar

jjulian at questor in /tmp/foo.mnt 
$ df -h .
Filesystem      Size  Used Avail Use% Mounted on
none             16G  5.1G   11G  32% /tmp/foo.mnt