Performance Center and VMWare

What is the official word from HP on PC and virtualization? Well, according to KM752992 in the HP Knowledge Base:

The following considerations apply when planning the deployment of Performance Center and/or LoadRunner within a virtualized environment:

1. Load Generator:
   This component can be affected by timing issues that result from being operated within a virtual environment. As a consequence it is not recommended to run the Load Generator for load testing purposes in a Virtual Environment when timing accuracy is a key requirement.For example, in the case of VMware’s ESX virtualization technology, there are issues in relation to the accuracy of the system clock that the operating system uses for time management. In physical hardware, the operating system can use hardware clock cycles to determine (relative) system time. This direct link is broken when using virtual machines as ESX now hands out CPU cycles in accordance with its management of system resources.This means that when using VMware (or other virtualization technologies where applicable) there is the potential for the accuracy or precision of time measurements (e.g. transaction response time) to be reduced. When deploying load generators on virtual machines the level of accuracy required should be considered and a physical hardware platform utilised to run this component if accurate measurement data (e.g. milliseconds) must be captured. Where the requirement is for lower levels of measurement accuracy (e.g. seconds) virtual machines can be used for this component.Furthermore it is worth noting that in environments where multiple load generators are in use and where accurate timing is required the best practice is that each load generator system is implemented using a common hardware and software platform so that these systems are equivalent. This avoids any differences in timing occurring during load tests. If load generators are implemented within a virtualized environment it will be difficult to ensure at all times that the system resources that are made available to each virtualized load generator are equivalent.
2. Controller:
   This component can be implemented within a virtualized environment. However in some cases where timestamp offsets are applicable, the level of precision obtained within a virtual environment will be reduced in a similar way to that described above for load generators. Therefore again if accurate timing is required it may be necessary to utilize a physical hardware platform for this component.
3. User & Admin Site:
   These components can be implemented within a virtual environment given that their role is primarily to manage and support the performance testing solution.
4. File Server:
   This component can be implemented within a virtual environment given its supporting role to management of the performance testing solution.
5. Database Server:
   This component can be implemented within a virtual environment given its supporting role to management of the performance testing solution.
6. VuGen:
   Apart from possible timing issues which may not be a critical consideration when developing scripts, this component can be implemented within a virtual environment.
7. Analysis:
   Given that the analysis of load testing results is not time dependent, this component can also be implemented within a virtual environment.

The following reference provides more information with respect to the timing issue for VMware virtualisation technology:

http://www.vmware.com/pdf/vmware_timekeeping.pdf

An additional aspect to also consider is the licensing of the product and how that may be affected by it’s use within a virtualized environment – in particular with respect to the range of operations that are available when managing virtual machines. This may be an issue depending on the virtualization technology chosen and the applicable licensing model.