Fio was originally written to save me the hassle of writing special test case
programs when I wanted to test a specific workload, either for performance
reasons or to find/reproduce a bug. The process of writing such a test app can
be tiresome, especially if you have to do it often. Hence I needed a tool that
would be able to simulate a given I/O workload without resorting to writing a
tailored test case again and again.
A test work load is difficult to define, though. There can be any number of
processes or threads involved, and they can each be using their own way of
generating I/O. You could have someone dirtying large amounts of memory in an
memory mapped file, or maybe several threads issuing reads using asynchronous
I/O. fio needed to be flexible enough to simulate both of these cases, and many
more.
Fio spawns a number of threads or processes doing a particular type of I/O
action as specified by the user. fio takes a number of global parameters, each
inherited by the thread unless otherwise parameters given to them overriding
that setting is given. The typical use of fio is to write a job file matching
the I/O load one wants to simulate.
