Why is (free_space + used_space) != total_size in df? [migrated]

Posted by Timothy Jones on Server Fault See other posts from Server Fault or by Timothy Jones
Published on 2011-11-28T23:52:49Z Indexed on 2011/11/29 1:53 UTC
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linux

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ext4

I have a ~2TB ext4 USB external disk which is about half full:

$ df 
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sdc             1922860848 927384456 897800668  51% /media/big

I'm wondering why the total size (1922860848) isn't the same as Used+Available (1825185124)? From this answer I see that 5% of the disk might be reserved for root, but that would still only take the total used to 1921328166, which is still off. Is it related to some other filesystem overhead?

In case it's relevant, lsof -n | grep deleted shows no deleted files on this disk, and there are no other filesystems mounted inside this one.

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