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.