STB Suite

Measuring Queue Depth with BAM

How can you know if command tag queuing is occurring during disk testing? And if it is occurring how do you know what depth of queuing is being achieved? The answer, if you have SCSItoolbox Suite version 6 is BAM!


As an example, we will configure the Disk Manufacturing Module to run a write/read test and ask it to try to keep 255 commands outstanding. Here is the DMM test configuration that we will run – with the requested queue depth of 255 highlighted:



Using BAM we can monitor in real time what the highest queue depth achieved is, and also what the current queue depth is. In a good test environment the current queue depth should stay high throughout the test. Here is a picture of the BAM real time monitor “speedometers”, one of which shows Queue Depth information:



Please note that the current queue depth is 0 because this screenshot was taken after the test finished.


Post capture analysis using the Trace Performance Analysis tab also shows the highest queue depth attained during the capture:



And the I/O Statistics page also shows the maximum queue depth for each individual drive



In summary, BAM provides real-time monitoring of command queue depth, along with post capture analysis which enables you to insure that the peripheral under test is achieving the queue levels that you require.