Sometimes when I hear my hard drive grinding, and I am not doing anything special on my Macbook Pro, I’m wondering what process is suddenly using the disk so heavily. I had been looking for a tool that would tell me what processes are causing the disk I/O’s for a while when I discovered that there is a command is OS X to find that out. You simply have to issue the /usr/bin/iotop in a shell. You have to be super user to use that command.