Bonnie++ read/write speed
Lets start our analysis by evaluating sequential read/write speed and CPU usage with the Bonnie++ benchmark:
Things seems pretty similar here, with the exception of somewhat higher ext3 CPU load. What about random seeks performance?
When not synching each request, all filesystems were equal. However, once we issue a sync command after each operation, btrfs is significantly slower and CPU-hungry then anything else. Some file type (eg: virtual machine images and large audio/video files) are often used with direct I/O (bypassing the O.S. page cache). Did the benchmarks depict a different picture in this case?
While sequential output (read) speed take a hit across the board, the most penalized filesystem seems to be btrfs. The high CPU load is a consequence of bypassing the operating system's cache.
On the other side, random seek speeds are largely unaffected, as they depend more on the hard disk / filesystem combo than on access mode.