"For those that have yet to read about the EXT4
file-system, it has several advantages over its predecessor, EXT3,
but it's more along the lines of just an update and not a complete
overhaul. In fact, EXT4 is both forward and backwards compatible
with EXT3. One of the major differences between EXT4 and EXT3 (and
EXT2 for that matter) is the introduction of Extents. The Extents
feature replaces block mapping, which is designed to improve
performance with the creation of larger files, and will reduce
fragmentation on the hard disk. Extents are similarly used within
Reiser4, XFS, and Apple's HFS+. Some of the other features for EXT4
include delayed allocation, persistent pre-allocation, and journal
check summing. The EXT4 file-system supports partition sizes up to
1 Exabyte and up to 640,000 sub-directories per directory.
"While the EXT4 file-system was marked as "ext4dev" within the
kernel to signify its development status, Red Hat has been shipping
EXT4 as an install-time option since Fedora 9. This support has
continued into Fedora 10 with the newest kernel components. When
installing Fedora, to create an EXT4 file-system you must append
"ext4" to the boot line when starting the Anaconda installer.
Beyond the Fedora option, EXT4 has yet to find itself as an option
in many distribution installers.
"For our testing we had compared the performance of the EXT3,
EXT4, XFS, and ReiserFS file-systems. We had done standard installs
of Fedora 10 x86_64 and each time we went without using a Logical
Volume Manager and the SWAP size was constant at 4GB. Fedora 10 was
reinstalled each time and we had just changed the default /
file-system to what was being tested and let that occupy the
remaining disk space. All file-systems were left with their
defaults, which does include the use of Extents on EXT4. Fedora 10
was left at its defaults except for disabling SELinux. The Serial
ATA hard drive was using AHCI mode."