What's causing all that disk I/O on my Mac?

After doing a full re-install of my MacBook Pro a few weeks back to combat system slowness, I’m again struck with a slow system. The problem is that there’s a lot of disk I/O going on. CPU and memory are fine. I’m just not sure what’s causing this trouble. Luckily, there’s an easy solution to find out what’s doing disk I/O on you mac. Open up a terminal and run