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I'm formatting a disk with following command switches, I can format the disk to ext4.

sudo mke2fs -F -E lazy_itable_init=0,lazy_journal_init=0,discard -t ext4 -b 4096 ...

However, once I added this switch:

-O ^has_journal

It will be formatted to ext2. Could you explain why?

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Because ext4 is an extension of the ext2 and ext3 filesystems; one of the features that it extended was the use of a journal.

References:

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  • So, you are saying, by disabling the journal feature, I'm installing a subset of ext4, that is why it is only shown as ext2? What I really want to know is, does this volume have all other advantages from ext4. Thanks! Commented Apr 13, 2016 at 0:57
  • I can't speak to the details of ext4, but I suspect that is why it's displaying as ext2 -- without a journal, it can't be called ext4. See also man mkfs.ext4 where it says: and "mke2fs -t ext3 -O ^has_journal /dev/hdXX" will create a filesystem that does not have a journal and hence will not be supported by the ext3 filesystem code in the Linux kernel.)" Commented Apr 13, 2016 at 14:20

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