ext4: How to account for the filesystem space?
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.
Edit: As requested, here's the output of
tune2fs -l /dev/sdc
tune2fs 1.41.14 (22-Dec-2010) Filesystem volume name: big Last mounted on: /media/big Filesystem UUID: 5d9b9f5d-dae7-4221-9096-cbe7dd78924d Filesystem magic number: 0xEF53 Filesystem revision #: 1 (dynamic) Filesystem features: has_journal ext_attr resize_inode dir_index filetype needs_recovery extent flex_bg sparse_super large_file huge_file uninit_bg dir_nlink extra_isize Filesystem flags: signed_directory_hash Default mount options: (none) Filesystem state: clean Errors behavior: Continue Filesystem OS type: Linux Inode count: 122101760 Block count: 488378624 Reserved block count: 24418931 Free blocks: 480665205 Free inodes: 122101749 First block: 0 Block size: 4096 Fragment size: 4096 Reserved GDT blocks: 907 Blocks per group: 32768 Fragments per group: 32768 Inodes per group: 8192 Inode blocks per group: 512 Flex block group size: 16 Filesystem created: Wed Nov 23 14:13:57 2011 Last mount time: Wed Nov 23 14:14:24 2011 Last write time: Wed Nov 23 14:14:24 2011 Mount count: 2 Maximum mount count: 20 Last checked: Wed Nov 23 14:13:57 2011 Check interval: 15552000 (6 months) Next check after: Mon May 21 13:13:57 2012 Lifetime writes: 144 MB Reserved blocks uid: 0 (user root) Reserved blocks gid: 0 (group root) First inode: 11 Inode size: 256 Required extra isize: 28 Desired extra isize: 28 Journal inode: 8 Default directory hash: half_md4 Directory Hash Seed: 68e954e4-59b1-4f59-9434-6c636402c3db Journal backup: inode blocks