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I just saw an answer question about filesystems for embedded hardware on another Stack Exchange site. The question was "What file system format should I use on flash memory?" and the answer suggested the ext2 filesystem, or the ext3 filesystem with journaling disabled a'la tune2fs -O ^has_journal /dev/sdbX

This made me wonder... What would the advantage be to using ext3 (with journaling disabled) over ext2? As far as I understood, the only real difference between the two was the journal. What other differences between ext2 and ext3 are there?

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The journal is the difference. You can not have an ext3 filesystem without a journal. If you disable the journal, it becomes an ext2 filesystem again.

ext4 has a number of beneficial features and can run without a journal, making it a much better choice.

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  • That's what I thought. I have used both ext3 and ext4 and know how much better ext4 is... I guess then the only benefit of ext3 sans journal would be that you could re-enable the journal later...
    – Josh
    Jul 20, 2012 at 12:58
  • @Josh, as I said before, there is no such thing as "ext3 sans journal", that is simply ext2. You can add or remove the journal whether you started as ext3 or not.
    – psusi
    Jul 20, 2012 at 13:01
  • Oh, really? I didn't understand that, sorry for being dense. I mean I thought before I asked the question that the only difference was the journal, but I didn't realize you could just add a journal to an ext2 filesystem and bam! now it's ext3. That's pretty neat.
    – Josh
    Jul 20, 2012 at 13:10
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  • Online file system growth.
  • Htree indexing for larger directories
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  • Actually those features are part of ext2.
    – psusi
    Jul 20, 2012 at 12:56
  • @psusi Are you sure? ext2 Htree indexes were originally implemented for ext2 but the patch never made it to the official branch, so I would say that they are not in any standard ext2 implementation. I really did not find any reference of the online system growth other than by ext3.
    – Matteo
    Jul 20, 2012 at 13:37
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    Yep.... see /etc/mke2fs.conf. It lists resize and dir_index as defaults, applied to all flavors, including ext2. The only one ext3 adds is the journal.
    – psusi
    Jul 20, 2012 at 18:42
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In addition to FS journaling, there's an extra difference.

According to www.slashroot.in and Super User, ext3 explicitly zeroes out the block pointers (in addition to the inode itself) upon file deletion, which ext2 doesn't do. This makes an essential difference on file recovery, but who relies so much on that?

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