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fsqual - file system qualification tool for asynchonus I/O

About

Linux AIO is notoriously bad; but it is hard to understand what the weaknesses of a filesystem implementation in a particular kernel version are. The fsqual tool provides a way to qualify a filesystem's aio implementation.

See this blog post for more information.

The test matrix checks the following variations:

  • Whether the write changes the size of the file or not
  • Whether the write first touches its offset range, or alternatively overwrites already-written data
  • Whether the write uses sector granularity (typically 512 bytes) or block granularity (typically 4096 bytes)
  • Whether the writes happen concurrently, or only one at a time
  • Whether O_DSYNC is in use (as is typical for commitlogs) or not

Building

Install the following packages:

  • libaio-devel (libaio-dev on Debian and derivatives)
  • xfsprogs-devel.x86_64 (xfslibs-dev on Debian and derivatives)
  • gcc-c++ (g++ on Debian and derivatives)
  • make

To build, simply run

make

Running

Change to a directory under the mountpoint to be tested, and run fsqual.

fsqual will report, for each test scenario, whether io_submit was truly asynchronous. This is done by measuring context switches during the io_submit call.