To store personal data, I have encrypted a partition with LUKS but, according to the file manager, the resulting encrypted device is much smaller: 334 GB versus 385 GB. However, the Disk Utility in Debian says the encrypted device is 385 GB. The file manager itself, before mounting the partition, says that it is 385 GB.

I have formatted the encrypted device with ext4. In case I missed something, here is how I have created, formatted and mounted the device:

# cryptsetup --verify-passphrase --verbose luksFormat /dev/sdc3

This will overwrite data on /dev/sdc3 irrevocably.

Are you sure? (Type uppercase yes): YES
Enter LUKS passphrase: 
Verify passphrase: 
Command successful.
# cryptsetup luksOpen /dev/sdc3 data
Enter passphrase for /dev/sdc3: 
# mkfs.ext4 /dev/mapper/data
mke2fs 1.41.12 (17-May-2010)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
23470080 inodes, 93873669 blocks
4693683 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=0
2865 block groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
Superblock backups stored on blocks: 
    32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 
    4096000, 7962624, 11239424, 20480000, 23887872, 71663616, 78675968

Writing inode tables: done                            
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 33 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.

Then the file manager allows me to mount the partition. I have also tried to mount the partition manually:

# mount /dev/mapper/data /media/data

But the size difference is still there. Closing and reopening the device does not help.

Any suggestions? Thanks.


  • Operating System: Debian GNU/Linux 6

  • File Manager: Nautilus 2.30.1

  • Disk Utility 2.30.1

  • So, ext4 has reserved 5% for its own purposes. Still there is a lot of space missing. Maybe it is a bug in Gnome regarding byte conversions (sorry, but I can't find the article where I read this).
    – Eleno
    Jun 16, 2014 at 13:32

1 Answer 1


Reason may be a few:

  1. A calculation way - base of prefixes (1000 vs. 1024)

    334*1024*1024*1024/(1000*1000*1000) = 358.63

    You can check disk and partitions size by:

    fdisk -l /dev/sdc

  2. Linux file systems reserving (by default) 5% (mkfs.ext4 -m PERCENT) free space accessed only by root (partition overflow protection)

  3. File system structures have some size (e.g. superblocks, journals etc)

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