-been transfered, unless limited by other options (\fBruntime\fR, for instance).
-Unless \fBnrfiles\fR and \fBfilesize\fR options are given, this amount will be
-divided between the available files for the job. If not set, fio will use the
-full size of the given files or devices. If the the files do not exist, size
-must be given. It is also possible to give size as a percentage between 1 and
-100. If size=20% is given, fio will use 20% of the full size of the given files
-or devices.
+been transferred, unless limited by other options (\fBruntime\fR, for instance,
+or increased/descreased by \fBio_size\fR). Unless \fBnrfiles\fR and
+\fBfilesize\fR options are given, this amount will be divided between the
+available files for the job. If not set, fio will use the full size of the
+given files or devices. If the files do not exist, size must be given. It is
+also possible to give size as a percentage between 1 and 100. If size=20% is
+given, fio will use 20% of the full size of the given files or devices.
+.TP
+.BI io_size \fR=\fPint "\fR,\fB io_limit \fR=\fPint
+Normally fio operates within the region set by \fBsize\fR, which means that
+the \fBsize\fR option sets both the region and size of IO to be performed.
+Sometimes that is not what you want. With this option, it is possible to
+define just the amount of IO that fio should do. For instance, if \fBsize\fR
+is set to 20G and \fBio_limit\fR is set to 5G, fio will perform IO within
+the first 20G but exit when 5G have been done. The opposite is also
+possible - if \fBsize\fR is set to 20G, and \fBio_size\fR is set to 40G, then
+fio will do 40G of IO within the 0..20G region.