How to Account for Filesystem Space in ext4

disk-usageext4filesystems

I've recently formatted a 1.5 TB drive with the intention of replacing ntfs with ext4.

Then I noticed that the files I saved don't fit on the new partition.

df:

ext4 (ext3 & ext2 show the same behavior)
Filesystem      1K-blocks   Used  Available Use% Mounted on
/dev/sdb1      1442146364   71160 1442075204    1% /media/Seagate

ntfs (similar to all other options that gparted offers):
/dev/sdb1      1465137148  110700 1465026448    1% /media/Seagate

That 1K-blocks difference means a glaring 22 GiB less usable space.

I have already executed

tune2fs -O \^has_journal
tune2fs -r 0
tune2fs -m 0

with, unsurprisingly, no effect as that does not affect blocks that just aren't there.

Still, fdisk reports that the ext4 partition covers the entire disk.

fdisk -l /dev/sdb:

WARNING: GPT (GUID Partition Table) detected on '/dev/sdb'! The util fdisk doesn't support GPT. Use GNU Parted.

Disk /dev/sdb: 1500.3 GB, 1500301910016 bytes
255 heads, 63 sectors/track, 182401 cylinders, total 2930277168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000
   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1               1  2930277167  1465138583+  ee  GPT

And thus e. g. resize2fs reports that there's "Nothing to do!"

dumpe2fs -h /dev/sdb1:
dumpe2fs 1.41.14 (22-Dec-2010)
Filesystem volume name:   <none>
Last mounted on:          <not available>
Filesystem UUID:          d6fc8971-89bd-4c03-a7cd-abdb945d2173
Filesystem magic number:  0xEF53
Filesystem revision #:    1 (dynamic)
Filesystem features:      ext_attr resize_inode dir_index filetype 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:              91578368
Block count:              366284288
Reserved block count:     0
Free blocks:              360518801
Free inodes:              91578357
First block:              0
Block size:               4096
Fragment size:            4096
Reserved GDT blocks:      936
Blocks per group:         32768
Fragments per group:      32768
Inodes per group:         8192
Inode blocks per group:   512
Flex block group size:    16
Filesystem created:       Sat May 21 17:12:04 2011
Last mount time:          Sat May 21 17:15:30 2011
Last write time:          Sat May 21 17:24:32 2011
Mount count:              1
Maximum mount count:      32
Last checked:             Sat May 21 17:12:04 2011
Check interval:           15552000 (6 months)
Next check after:         Thu Nov 17 16:12:04 2011
Lifetime writes:          1372 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
Default directory hash:   half_md4
Directory Hash Seed:      c334e6ef-b060-45d2-b65d-4ac94167cb09
Journal backup:           inode blocks

What is using that missing space?

Best Answer

Let's see. The device size is 1,465,138,583½ kB = 1,500,301,909,504 B. The filesystem consists of 366,284,288 blocks of 4096 B each, which is 1,500,300,443,648 B. I don't know what the remaining 1,465,856 B (1.4 MB) are used for (additional copies of the superblock? I know there are a few kB of space at the beginning for the bootloader.).

The filesystem contains 91,578,368 inodes of 256 bytes each, which takes up 23,444,062,208 B (about 22 GB, hint, hint). Then there is 1,442,146,364 kB = 1,476,757,876,736 B for file contents. This accounts for 23,444,062,208 B + 1,476,757,876,736 B = 1,500,201,938,944 B. The remaining size is 98,504,704 B = 24,029 blocks which is in the right range to be the journal size.

As you can see, everything is accounted for. (Ok, almost everything, but we're talking megabytes, not gigabytes.)

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