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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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up vote 5 down vote accepted

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 '12 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 '12 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 '12 at 13:10
  • Online file system growth.
  • Htree indexing for larger directories
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Actually those features are part of ext2. – psusi Jul 20 '12 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 '12 at 13:37
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 '12 at 18:42

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