Here are a few utilities that monitor disk I/O performance.
iostat -d 5 pidstat -dl 20 iotop --only
The alternative is atop, which you can set to run every 10 seconds for 3 hours. The output can be viewed later.
atop -a -w logfile.atop 10 10800 &
Use atop to read the log file.
atop -r /path/to/logfile.atop