rm files, files gone, but df -k, doesn't show the right free space

[Guest]

I am doing some cleanup of files doing mix of rm, rm -r, rmdir. After
files have been deleted, I'm trying to guage free space using df -k.
For example dmn1 contains 30 file systems. When I go to fs1 (in dmn1)
delete one of 2 large files, do a df -k, free space doesnt show. In df
-k, shows 12GB used, doing a du -sk in the folder shows only 6GB used.
The file i deleted was 6GB. Yesterday, the files i was deleting freed
up space. Today i delete the files, space isnt showing up. Happening
to multiple file systems on one domain. FYI, one node of a cluster.

[Guest]

nevermind, even though i unmounted the db files, once i stopped the db
engine, it freed up the space

[Google]