strange behaviour of df command

["Atul Tyagi" <tyagi atul gmail com>]

Hi All,

I am facing a little problem. I guess its more of a conceptual problem
rather than a OS issue.

One of my software raid partiton /dev/md4 is about 30 GB. I had put a file
of about 18GB in that jus for few mins and then deleted that. Now even after
about 6 hrs. My RHEL4 system gives me weird output. following are the
outputs that might help you understand.

df -h
===

[root pingu ~]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/md0              5.0G  2.7G  2.1G  56% /
/dev/md1               99M   17M   78M  18% /boot
none                 1014M     0 1014M   0% /dev/shm
/dev/md2              5.0G  190M  4.5G   4% /var
/dev/md4               30G   22G  5.9G  79% /usr/local/test

du -hs
=====
[root pingu ~]# du -hs /usr/local/test
2.7G    /usr/local/test

Can some one please clear my doubt and explain why there is a such a hugh
difference in both the commands. Disk usage shown by df -h is 22G where as
du shows 2.7G.

Would appriciate any pointer to this problem.

Thanks,

Atul