As its name indicates, iotop is a top-like utility but for disk I/O. It shows a constantly updating list of processes, sorted by the amount of disk IO (read or write) they are performing. I find it useful to find out quickly which process is causing the disk to grind noisily. 😊
$ sudo apt install iotop
$ sudo iotop
Note how the tool requires root privileges to run.
$ sudo iotop -o
$ sudo iotop -d 2
Tried with: IOTop 0.6 and Ubuntu 14.04