By default for Windows Server 2008 and above, the default virtual SCSI controller is the LSI Logic SAS disk controller. It’s there for compatibility purposes, and piggybacks the existing driver that is built into the operating system. It works great because it always ‘just works’.
However, compatibility does not necessarily mean fastest, and the LSI SAS driver is a pretty good performer, but VMware developed an alternative that can boost performance for virtual machines with high I/O requirements. It is called the Paravirtual SCSI (PVSCSI) driver, and it is included with the VMware Tools package that should be installed into every VMware-based virtual machine. This driver was designed by VMware to improve the raw performance of every virtual disk connected to it. On average, I experience a 12% throughput performance improvement, lower latency to the underlying storage, and lower CPU associated with storage handling when using this driver.
How can you take advantage of this driver?
It’s easy! Virtual disks are connected to virtual disk controllers. All we have to do is ensure that the VMware Tools are installed (so the driver is present) and then make a few changes to the VM configuration.
First, check out the virtual disk configuration of the VM. This example uses an older Windows Server 2008R2 VM. Almost always, one or more virtual disks are connected to the LSI SAS controller. See how the disk assignments are set to a SCSI ID of 0:0 and 0:1? This is how the old SCSI hardware configuration was emulated with the advenet of virtualization. The first number is the controller number, and the second is the SCSI channel assignment.
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