In complementing the earlier Linux 3.16 file-system tests on an SSD (and the later Btrfs testing), here are benchmarks of EXT4, XFS, and Btrfs from the Linux 3.15 and 3.16 kernels being compared from a traditional rotating hard drive.
As has become common practice at Phoronix, for each new development kernel we end up benchmarking the most commonly used, mainline Linux file-systems on a hard drive and solid state drive. With the SSD results out there in the aforelinked articles, in this article are results using a high-performance Western Digital HDD from a Core i7 Haswell system running Ubuntu and comparing the mainline stable Linux 3.15 kernel against a daily snapshot of Linux 3.16 from this week.
The HDD being tested on EXT4, XFS, and Btrfs was the 150GB Western Digital VelociRaptor WD1500HLHX-0. All three file-systems were tested on each kernel with their default mount options; the host was running Ubuntu 14.04 LTS. Benchmarks were conducted via the Phoronix Test Suite and the results can be found on the following pages.