With the EXT4 file-system being marked as stable in the forthcoming Linux 2.6.28 kernel, and some Linux distributions
potentially switching to it as an interim step until the btrfs file-system is ready, we decided it was time to benchmark this journaled file-system for ourselves.
We ran a number of disk-centric Linux benchmarks along with several of our real-world tests from the Phoronix Test Suite to gauge how well the EXT4 file-system performance will be noticed by desktop users and computer gamers. We have compared these EXT4 results to the EXT3, XFS, and ReiserFS file-systems.
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.
http://www.linuxlinks.com/portal/news/article.php?story=20081203132848260