" If however Ext3's successor encounters big problems with the
pre-release versions of Fedora 11, the developers will dump that
plan and revert to Ext3.
"So the Fedora Project is going one step beyond Ubuntu version
9.04 (Jaunty Jackalope), which as things currently stand will offer
Ext4 as an install time option, though the installer will still use
Ext3 as its default file system. The same was true of Fedora 9 and
10: the "ext4" parameter needed to be used when booting up the
installation media, in order to enable that file system in the
installer. Ext4 was still experimental when Fedora 10 was
released."