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