[dm-crypt] cryptsetup creates 1.8 Gb when it should be 1Tb

metageek pedro at gepasi.org
Mon Oct 28 03:05:23 CET 2013

I've checked the FAQ, but this does not seem to be answered there...

I'm creating an encrypted partition on a portable USB3 drive. The drive is
1Tb and I've allocated all on a single partition:

Disk /dev/sdb: 1000.2 GB, 1000204885504 bytes
255 heads, 63 sectors/track, 121601 cylinders, total 1953525167 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: 0x9f0bf2e1

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1              63  1953525166   976762552   83  Linux

Then I went on to create the LUKS encryption:

cryptsetup luksFormat /dev/sdb1

then open it:

cryptsetup luksOpen /dev/sdb1 pjhomecrypt

now using status to see its properties:

cryptsetup -v status pjhomecrypt         
/dev/mapper/pjhomecrypt is active.
  type:    LUKS1
  cipher:  aes-cbc-essiv:sha256
  keysize: 256 bits
  device:  /dev/loop0
  loop:    /dev/sdb1
  offset:  4096 sectors
  size:    3752880 sectors
  mode:    read/write
Command successful.

I see there are only 3752880 sectors at 512 bytes, this is only about 1.8 Gb!

creating an ext4 filesystem on this, and mounting it shows the same...:

mkfs.ext4 /dev/mapper/pjhomecrypt
mke2fs 1.42.6 (21-Sep-2012)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
117360 inodes, 469110 blocks
23455 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=482344960
15 block groups
32768 blocks per group, 32768 fragments per group
7824 inodes per group
Superblock backups stored on blocks: 
        32768, 98304, 163840, 229376, 294912

Allocating group tables: done                            
Writing inode tables: done                            
Creating journal (8192 blocks): done
Writing superblocks and filesystem accounting information: done
mount /dev/mapper/pjhomecrypt /mnt
df -Th /mnt
Filesystem              Type  Size  Used Avail Use% Mounted on
/dev/mapper/pjhomecrypt ext4  1.8G  2.7M  1.7G   1% /mnt

So I only have 1.8Gb out of the 1Tb drive.
I've googled and can't find anyone with similar problems, so I must be
missing something here, though I haven't figured it out.

Can anyone help here?

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