hard-link question

[Umarzuki Mochlis <umarzuki@gmail.com>]

this output is before i hard-linked a 4.4 MB mp3 file

$ df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda2            677688728 112432972 531334324  18% /
tmpfs                  1987692         0   1987692   0% /lib/init/rw
udev                   1981764       244   1981520   1% /dev
tmpfs                  1987692         4   1987688   1% /dev/shm
/dev/sda1               297560     49172    233028  18% /boot

this is after hard-linked that file

umarzuki@v470:~/Videos$ df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda2            677688728 112432940 531334356  18% /
tmpfs                  1987692         0   1987692   0% /lib/init/rw
udev                   1981764       244   1981520   1% /dev
tmpfs                  1987692         4   1987688   1% /dev/shm
/dev/sda1               297560     49172    233028  18% /boot

this is after I deleted the original mp3 file

umarzuki@v470:~/Videos$ df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda2            677688728 112432996 531334300  18% /
tmpfs                  1987692         0   1987692   0% /lib/init/rw
udev                   1981764       244   1981520   1% /dev
tmpfs                  1987692         4   1987688   1% /dev/shm
/dev/sda1               297560     49172    233028  18% /boot

i can still play the mp3 file.
Why is that the used space is reduced (/dev/sda2) after I hard-linked
that mp3 file?
Why is that the used space is increased after I deleted the source mp3 file?

-- 
Regards,

Umarzuki Mochlis
http://debmal.my