This repository contains a comprehensive set of IO benchmarks for Linux and OS X. These benchmarks are intended to determine the fastest ways to perform the following IO operations on each target platform:

• Sequentially reading a file.
• Sequentially overwriting a preallocated file.
• Replacing the contents of an existing file with those of another file.

• Linux (version 2.6.33 or newer) or OS X.
• A C++11-conformant compiler that accepts flags in GCC's format (e.g. g++ or clang++).
• Boost.
• Ruby.
• Rake.

Before compiling the benchmarks, you will need to set two environment variables.

• Set CXX to your desired C++11-conformant compiler.
• Set BOOST_INCLUDE_PATH to the path containing the Boost header files.

Afterwards, you can compile the benchmarks by running rake.

The tools directory contains a set of scripts that you will need to run the benchmarks. In order to run these scripts, you will need to type chmod +x tools/*.

• The tools/make_data.rb script uses dd to create a set of files in the data directory. These files are used to perform the benchmarks.
• The tools/test_read.sh and tools/test_write.sh scripts perform the reading and writing benchmarks, respectively.
• The read benchmark must be run as root! This is because the benchmark repeatedly drops the page cache to obtain accurate results. Do not run this benchmark on a server that is doing anything important!
• I did not create a script to run the copy benchmark. Based on existing results, it is clear that the fastest way to copy a file on OS X is copy_mmap, and splice_preallocate_fadvise or sendfile_preallocate_fadvise on Linux.

In both test_read.sh and test_write.sh, you will see the following lines:

#sizes=(8 16 24 32 40 48 56 64 80 96 112 128 160 192 224 256 320 384 448 512 640 768 896 1024)
sizes=(8 16 32 64 80 96 112 256) #512 1024)

These lines declare the sizes of the files (in megabytes) that are used for the benchmarks. By default, only a small set of files ranging in size from 8 MB to 256 MB are used. The first line in the pair refers to the full set of files produced by tools/make_data.rb. Even on a machine with a fast PCIe SSD, the read benchmark did not finish overnight. So only uncomment this line if you know that you will be able to leave the benchmark running for a long time (half a day to several days, depending on the speed of your hard drive).

The results of the benchmarks are saved in the results directory. This directory already contains results generated from a couple of systems.

This project is released under the Creative Commons Attribution 4.0 International License.

• The manual pages for OS X and Linux.
• A very useful benchmark on write patterns.
• The blog post by the same author.
• A Mozilla blog post about F_PREALLOCATE on OS X.