According to Ted Ts'o (maintainer of ext4): "the main reason why we did the ext3 -> ext4 fork was that adding 64-bit numbers required major surgery, and we didn

According to Ted Ts'o (maintainer of ext4): "the main reason why we did the ext3 -> ext4 fork was that adding 64-bit numbers required major surgery, and we didn't want to break a lot of production users who were using ext3. But from a file system format perspective, ext2, ext3, and ext4 are the same logical file system." (http://article.gmane.org/gmane.linux.file-systems/97986 http://article.gmane.org/gmane.linux.file-systems/97986)