"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."
