[CentOS] HDD usage oddity

Thu Nov 22 01:16:32 UTC 2007
Stephen Harris <lists at spuddy.org>

On Wed, Nov 21, 2007 at 07:37:31PM -0500, Ugo Bellavance wrote:
> 	2 of my Centos4 servers are showing weird behavior.
> [root at server1 ~]# du -sh /var/
> 1.8G    /var/
> [root at server1 ~]# df -h /var
> Filesystem            Size  Used Avail Use% Mounted on
> /dev/sda7             4.3G  3.9G  181M  96% /var

There are two things to consider.


If you have large block sizes and lots and lots of small files then
"du" will report a number quite a lot smaller than "df".  "df" reports
on actually amount free; "du" reports on apparent size of the files used.


If you delete a file that is still "open" (typically a log file, or
a file being written to in /var/tmp) then Unix doesn't actually delete
the file at that point; it removes the directory entry and marks the file
to be deleted when no one is using it any more.

I've seen developers create debug logs in /tmp that grew to 2Gb then
delete them to save space... while the program was still writing more
debug messages, so they didn't save any space at all.