How can I monitor disk I/O in a particular directory?

I’ve got a few processes with a known name that all write to files in a single directory. I’d like to log the number of disk block reads and writes over a period (not just file access) to test whether a parameter change reduces the amount of I/O significantly. I’m currently using iostat -d -p, but that is limited to the whole partition.

How can I see what processes are running?

I use Ubuntu Server 10.10 and I would like to see what processes are running. I know that PostgreSQL is running on my machine but I can not see it with the top or ps commands, so I assume that they aren’t showing all of the running processes. Is there another command which will show all running processes or is there any other parameters I can use with top or ps for this?