Possible Duplicate: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/bigI'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/sdctune2fs 1.41.14 (22-Dec-2010)Filesystem volume name:   bigLast mounted on:          /media/bigFilesystem UUID:          5d9b9f5d-dae7-4221-9096-cbe7dd78924dFilesystem magic number:  0xEF53Filesystem 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_isizeFilesystem flags:         signed_directory_hash Default mount options:    (none)Filesystem state:         cleanErrors behavior:          ContinueFilesystem OS type:       LinuxInode count:              122101760Block count:              488378624Reserved block count:     24418931Free blocks:              480665205Free inodes:              122101749First block:              0Block size:               4096Fragment size:            4096Reserved GDT blocks:      907Blocks per group:         32768Fragments per group:      32768Inodes per group:         8192Inode blocks per group:   512Flex block group size:    16Filesystem created:       Wed Nov 23 14:13:57 2011Last mount time:          Wed Nov 23 14:14:24 2011Last write time:          Wed Nov 23 14:14:24 2011Mount count:              2Maximum mount count:      20Last checked:             Wed Nov 23 14:13:57 2011Check interval:           15552000 (6 months)Next check after:         Mon May 21 13:13:57 2012Lifetime writes:          144 MBReserved blocks uid:      0 (user root)Reserved blocks gid:      0 (group root)First inode:              11Inode size:           256Required extra isize:     28Desired extra isize:      28Journal inode:            8Default directory hash:   half_md4Directory Hash Seed:      68e954e4-59b1-4f59-9434-6c636402c3dbJournal backup:           inode blocks
Why is (free_space + used_space) != total_size in df?
linux;ext4
Theres no missing space. 5% reserved is rounded down to the nearest significant figure.1k Blocks: 1922860848Reserved 1k Blocks: (24418931 * 4) = 97675724Total blocks used: 927384456 + 897800668 + 97675724 = 1922860848Edit: Regarding your comment on the difference between df blocks and 'Block Count' blocks.So the 4k block difference is (1953514496 - 1922860848)/4 = 7663412The majority of the 'difference' is made up of the Inode blocks per group parameter which is 512. Since there is 32768 blocks per group that puts the number of groups at 488378624 / 32768 which is 14904 rounded down. Multiplied by the 512 blocks it takes up gives 7630848 blocks.That gives us 7663412 - 7630848 = 32564 unaccounted for. I assume that those blocks make up your journal size, but not too sure on that one!