So what's there to gather from these tests? EXT4 isn't a file-system to trench all other Linux file-systems, but that's to be expected as otherwise there would not be significant resources going into btrfs. EXT4 is, however, a nice update based on EXT3 that makes it an appealing step-in solution. While maintaining forwards and backwards compatibility with this Linux file-system that has been in the mainline kernel for nearly eight years, EXT4 introduces Extents to replace the block mapping scheme used on earlier generations of the extended file-system, persistent pre-allocation, delayed allocation, precision timestamps, and journal check summing.
Between our Bonnie++, IOzone, and Flexible IO Tester test trials, the EXT4 file-system had exhibited the best performance in five of the eight tests. SGI's XFS file-system was in first the other three times. While this shows the abilities of each file-system, it doesn't mean much unless your job consists of running disk benchmarks day-in and day-out.
In Nexuiz, World of Padman, and Unreal Tournament 2004 to represent gaming on the Linux operating system, the results were virtually identical. To the Linux gamer, switching to EXT4 or XFS will not really mean much in the way of improved frame-rates. If though you deal with compressing files often, of the four file-systems tested, the best appears to be EXT4 or XFS. When it came to multimedia encoding, we cannot call a decisive winner. In our GnuPG encryption test, EXT3 was the fastest followed by XFS. However, in the Bork encryption test, EXT4 was the fastest followed by EXT3. EXT3 does still appear to have some advantages.
EXT4 is clearly a significant improvement over EXT3 when it came to the pure disk benchmarks, however, in the real world, saying better performance should not be used as a reason to replace your existing EXT3 or XFS partitions. In our tests that cater towards Linux desktop users and gamers, EXT4 hadn't delivered a sizable quantitative advantage. That's not to say though it's not worth switching to EXT4. EXT4 is more scalable, more efficient through the use of Extents, supports larger disk capacities, can handle twice the number of sub-directories, is capable of handling online defragmentation, and there is improved reliability via journal checksums. What perhaps is more important is that with the addition of these new features, the performance hasn't regressed. Also, when testing the EXT4 file-system, we hadn't run into any problems with stability, file corruption, or any other issues.
EXT4 is declared stable in the soon to be released Linux 2.6.28 kernel, but from there it isn't clear how big of a role EXT4 will play within the Linux ecosystem. Chances are we would see it be adopted officially by Fedora or another bleeding-edge distribution before it's used by default within Ubuntu or a commercially supported distribution. The development timeline for btrfs places a 1.0 release in Q4'08, but it doesn't look we'll see a stable release of that until next year. Depending upon how fast that file-system is hardened and what adoption rates it sees, it may largely influence how EXT4 fairs as a temporary alternative.
If you would like to run your own file-system benchmarks, check out the Phoronix Test Suite.