Using tools like iotop one can monitor the i/o of individual processes which is fine, but you do not find out which directory a process writes into. If the PID would always be the same that would not be a problem, one could strace or something else to find out which files are affected, or possibly
lsof +p <PID>
But I noticed chromium does some heavy disk writes when I open a video, despite the fact that I already put many directories associated with chromium on a tmpfs. Now I would like to find out which directories it writes to in the instant iotop shows the high i/o usage. Chromium does change the PID all the time, which makes this even more complex.