Let's suppose I create a file, map it to /dev/loop0, and create a LUKS partition inside

dd if=/dev/zero of=myfile bs=1M count=1000
losetup /dev/loop0 myfile 
cryptsetup -c aes-cbc-essiv:sha256 -s 256 -v -y luksFormat /dev/loop0

I then open the encrypted partition

cryptsetup luksOpen /dev/loop0 myfile

Now, I have my encrypted file appear as a disk /dev/mapper/myfile. I need to create a filesystem before I can use it.

Here is my question: Given that this my new filesystem-inside-file resides on another ext4 filesystem (which already is using journal), what options would be best for this new filesystem ?

Specifically, if I format my new filesystem-inside-file ext4, should I use journal?. Somehow, the idea of journal filesystem inside another journal filesystem seems not right to me, intuitively.

  • That's a bizarre setup. Why not use ecryptfs? – Gilles 'SO- stop being evil' Jan 18 '14 at 23:38
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    what are the advantages of eCryptfs over my solution? I don't know eCryptfs, so I cannot compare it. But the setup I am using is simple and transparent. – Martin Vegter Jan 19 '14 at 13:17

From my experience running an encrypted reiserfs with private information you should not put that on an journalling filesystem like ext3. I switched back from ext3 to having the file on an ext2 partition after I had to restore from a backup.

Over the years ( I have had this file for 5 years ), I had to run recovery several times, and when hosted on ext3 this was the only time reiserfsck could not recover. I think that was because ext3 did a recover which confused the internals of the encrypted disk.

I never tried a non-journal filesystem on a journal filesystem (e.g. encrypted ext2 file on reiserfs) for me the important (i.e. encrypted data should be journalled).

I am still running reiserfs, never used ext4 for this (but I am considering btrfs, just need to check some time if that is stable enough)

If you put your homedirectory on there, be prepared that this feels a bit sluggish, I don't think any finetuning with parameters could have helped that, and I don't think the ext4 ones will influence things much, given that encryption is a performance penalty hit in all directions.

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  • that is very interesting. Could you perhaps explain why you prefer reiserfs/btrfs above ext4 ? – Martin Vegter Jan 18 '14 at 10:18
  • @MartinVegter ReiserFS was the only option when I wanted a journaling filesystem, ext3 came years later. Btrfs seems the next major step. – Timo Jan 18 '14 at 10:23

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