You could also use iostat. I monitor my servers' disk i/o using iostat -xNm 1 10. The metrics await* and avgqu* are normally what I am interested in. They give

You could also use iostat. I monitor my servers' disk i/o using iostat -xNm 1 10. The metrics await* and avgqu* are normally what I am interested in. They give the disk wait timings for serving disk i/o requests. You also have access to the dtrace probes.