That's not true. The changes from ext4 to ext3 are evolutionary, not revolutionary. There is full backwards compatibility, and there's still a lot of the orig

That's not true. The changes from ext4 to ext3 are evolutionary, not revolutionary. There is full backwards compatibility, and there's still a lot of the original ext3 code in ext4 (in particular, we still support old-fashioned indirect blocks in ext4, even though it's not the default, and we do that using a copy of the ext3 code). If you look in the git history, you can see all of the changes as we added new features into ext3 during the course of the ext4 development.