Are there any real advantages of ext4 over ext2 ?

[Ihor Antonov]

> See:
> 
> https://en.wikipedia.org/wiki/Ext2
> 
> https://en.wikipedia.org/wiki/Ext4

Apart from some edge cases the only meaningful difference is jornaling. 
Ext2 is simple FS and does not have a journal, ext3 and ext4 can have 
journal (and they usually do by default) but it can be disabled.

They all are backwards compatible. You should be able to read ex2 volume 
with ext3/4 driver. But not sure if the other way works. It would be an 
interesting exercise to try to disable all possible features on ext4 
volume (like journal) and try to read it in read-only mode with ext2 
driver (but there is a high chance it might not work)


> I recently learned that FreeBSD supports ext2 and have formatted a USB 
> HDD with ext2 for this reason, but have yet to test it with FreeBSD.

> OpenZFS is available and works on both platforms.  But, I have not tried 
> moving ZFS devices between platforms.  I expect the crux would be 
> limiting the feature flags to the common subset.

OpenZFS does work across Linux/FreeBSD as long as you use common subset 
of features. I had to re-format my Linux ZFS drive recently because it 
had feature at dnodesize enabled, and FreeBSD does not support this feature 
yet.

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Ihor Antonov