Method for tracking and storing time to complete and average completion time for storage area network I/O commands

Embodiments of the present invention are directed to providing continuously updated completion time and an average completion time information for I/O commands on a per-LU, per-target, per-port basis. This measurement is performed by a kernel device driver that handles the I/O for the system at lower layers, so the measurements are more accurate because the delays due to higher level processing are not included. This approach allows the driver to track movements in the average I/O command completion time per LU and limit outstanding I/O counts early enough to potentially prevent overload conditions. By catching the overload early, the invention also has the ability to restore the original outstanding I/O count as the overload condition subsides.