iotop watches I/O usage and displays I/O bandwidth read/write usage for processes/threads. It will also display the percentage of time processes spent while swapping in and also waiting for I/O to complete. To install iotop on a Ubuntu system use:
sudo apt-get install iotop
The left/right arrow keys change the sort column order (process ID, PRIO, USER id, disk read, disk write, swapin activity, IO activity and command used). The 'r' key toggles the sort order and the 'a' key toggles the I/O display between bandwidth and accumulated I/O stats.
above, iotop running on my laptop
So, another top tool for you to use to track down rogue processes or I/O hoggers.