we use read(2) and write(2) for asynchronous
io.
+ null Doesn't transfer any data, just pretends
+ to. This is mainly used to exercise fio
+ itself and for debugging/testing purposes.
+
iodepth=int This defines how many io units to keep in flight against
the file. The default is 1 for each file defined in this
job, can be overridden with a larger value for higher