Workload Design and Behaviors

The SCSI Workloads (FC-SCSI, iSCSI) use a probability-based design to generate the user specified distribution of commands and load. Factors such as SUT performance, Test Bed, errors, and also runtime duration can cause the actual distribution and load to be very different from the expected distribution and load.

For example, if READ/WRITE ratio = 71%/29%, it means that READ probability is 0.71 and WRITE probability is 0.29 during the workload run. More precisely, this concept is applied to into 4 groups: sequential Read, sequential Write, random Read, and random Write. The “larger” your test environment is, the better a longer workload run duration should be configured as, from a probability perspective, it is more likely that the actual observation will match the configuration.

When you have multiple concurrent workers, each worker goes through its own “pass”, so you have many different workers doing different things on different files on the SUT. However, throughout the workload test run, the configured operations will eventually be performed with sufficient runtime duration, in the absence of unexpected errors or performance issues.

The Port Queue Depth also can place an upper limit on how many outstanding I/Os you can have. The Port Queue Depth setting is applied on a per Workload Generator Port basis. If MPIO is enabled, then the Ports that belong to the same MPIO Group “share” the Port Queue Depth setting. For example, if you have two Ports that are part of one MPIO Group, and your Port Queue Depth setting is 1,024, then there is not 2,048 for the two Ports combined, because the two Ports that are part of the same MPIO Group are treated as a single interface to the upper layer SCSI workload.