Can we use Load generators on Virtual machines?

Well of course we can, if it is just for the sake of using but this will alter the response time of the tests.

HP never recommends using VM’s and the HP guide states that the VMware's clock does not synchronize with the hardware clock. This causes inaccuracy in the response time obtained.

This implies that load test results are not showing the actual performance of the application as opposed to what it would be in the real world.

What is VM Clock drift?

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The term Clock drift describes situations where the reported time diverges from the correct time at an approximately constant rate.

There are two main reasons for this:

•  Time in a virtual machine drifts because the hardware time source used by the virtual machine monitor drifts
•  Time in a virtual machine drifts at a constant rate

The system clock in VM’s is also virtualized and occasionally has to re synchronize with the physical system clock. This system clock is tied to your virtual user timing directly and the amount of drift is unpredictable and ungovernable.