iotop is a python tool that shows how much I/O happens on the system. It's a lot more interesting than the vmstat 1 command, since it can display per-process I/O, thanks to the per-task storage I/O accounting feature in latest kernels (commit).

I've upload an iotop package in cooker, but our cooker kernels don't have TASK_IO_ACCOUNTING enabled, maybe we could have it in one of our contrib kernel packages.