df reports wrong free space for an Ext4 partition

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http://serverfault.com – My system is CentOS 6 x86_64 with root partition formatted as ext4. df reports around 3Gb as used space: Filesystem 1K-blocks Used Available Use% Mounted on /dev/md1 20158260 3433724 15700540 18% / but du -sm -x / claims less than a single Gb is used actually: [root@xxxx ~]# du -sm -x / 948 / I wonder what is going on here. Usage numbers changed right after reboot. The filesystem claims it's clean, no errors in logs. I found this, but it did not explain a root of the problem. Should I just reformat the partition? Is there any way to track down this ext (HowTos)