2. PERFORMANCE REPORTING ANALYSIS › 2.7 Graphic Analysis › 2.7.4 I/O Tracking Graphs › 2.7.4.2 Average MPL Waiting for Devices

2.7.4.2 Average MPL Waiting for Devices

GRAPHIC RESULTS

This graphic analysis provides a vertical bar chart for each
of one or more direct access devices that experienced the
highest queue times during the interval being charted.  The
default is to plot only the single device showing the highest
queue time, but you can choose to analyze more devices per
interval reported.  The bar chart represents the average
number of users of the device that were waiting to gain
access to it.

ANALYSIS GUIDELINES

Since this chart shows the average number of applications
waiting for a device, you can use it as a warning indicator.
The average number of applications waiting is a measurement
external to the application.  If an application such as one
processing online transactions internally queues its own
requests for a device, this delay will not show on this
chart.  This chart will show the queuing that occurs in the
I/O subsystem when it has received the I/O request, but is
holding it until a previous request that it is managing has
completed.

There is no necessarily good or bad number with this chart.
You should produce this chart frequently enough to be
accustomed to the queuing levels normally seen in your
environment.

The detailed behavior of I/O devices can be further analyzed
using the I/O Configuration analysis reports described in
Section 2.4.