Within virtual machines, there are different SCSI controllers available for writing the data to the actual disk. For the different operating systems, there are best practices which gives the best performance. Windows XP uses the BusLogic Parallel SCSI driver and the results are acceptable. With Windows 7 the commonly used controller is the LSI Logic SAS controller. Which is selected automatically when creating a virtual machine of this type.
Different vendors have different best practices, some of them advice to use the VMware Paravirtual SCSI controller. The VMware Paravirtual SCSI controller needs to be selected manually and needs some additional actions before it can be used. Creating a small additional disk with VMware Paravirtual SCSI controller connected will force the OS the use and installation of the correct driver. The additional drive can be removed after installation and the initial drive must be connected to the VMware Paravirtual SCSI controller.
The question is which of these controllers gives the highest performance. For that I have started some tests with IOmeter in a virtual Windows 7 machine. The first test was with the VMware Paravirtual SCSI controller and using an additional disk beside the system disk. The results of the test is show below:
The second test was performed with the LSI Logic SAS controller and was using the additional diks. This configuration could not give the same performance as the VMware Paravirtual SCSI controller, the results of this test are placed below
The other test we did was with the system disk instead of the additional disk. The same results are showed as the previous tests. The use of the VMware Paravirtual SCSI controller performs a little better then the LSI Logic SAS SCSI controller
The results of above are within the virtual machine, with Xangati i was able to measure from the outside. The following picture will show the light better performance of the VMware Paravirtual SCSI controller, where the first and last test includes the VMware Paravirtual SCSI driver:
For now, the conclusion can be drawn that the use of the VMware Paravirtual SCSI controller lead them a slight performance gain in these test.