Ubuntu: tool for displaying disk activity in general and by process
I can recommend iotop, which shows you exactly disk-read and disk-write in bytes per seconds, per process.
You can install it with sudo apt-get install iotop in Ubuntu.
Try atop. Start it and press d to show disk-related output.
You can try Saidar.
apt-get install saidar
Alternatively you could try one of these: http://www.upubuntu.com/2012/06/list-of-best-system-monitoring.html