Incorrect Disk space usage in Linux server

Question

I can see the used disk quota on server is 81G for partition /dev/sda3 mounted to '/' as follows.

Filesystem      Size  Used Avail Use% Mounted on
/dev/sda3       106G   81G   20G  81% /
tmpfs           1.9G     0  1.9G   0% /dev/shm
/dev/sda1       477M   52M  400M  12% /boot
tmpfs           1.0G     0  1.0G   0% /var/lib/mysqltmp
/usr/tmpDSK     4.0G  183M  3.6G   5% /tmp

But when Iam checking with the '/' directory by executing du -sh command it is taking only 17G of disk space, can any one advice where this remaining space is utilized, any advice ? Iam using CentOS release 6.7 (Final)

Answer 1

maybe processes have open handles on large files (like a dropped database). files may then seem deleted but space is not reclamined before all handles on these files are closed.

lsof may be your friend here.