ioprofile ( now called pt-ioprofile ) is a nifty tool for seeing the I/O activity of a process:
The ioprofile tool captures a process’s I/O activity through lsof and strace and summarizes it. The result is a tabular display that shows you where the process spent its time on I/O operations.
Here is a screenshot from the first example in the original ioprofile docs:
Which shows the time spent in I/O for each of those files. Another useful option is the see the byte count of I/O for each file:
