Feb 012018

I recently had a great question on some of the differences in virtual machine disk presentation from one of our amazing clients, and I thought I’d share the answer here because it’s a common question that I receive.

Some hypervisors (including some hyper-converged compute platform vendors who shall remain nameless) do not give you much flexibility in the way storage is presented to a VM. You pick the VM and click to add drives. That’s it. No knobs to turn, no mess, no fuss. It’s meant to be easy, and for almost all situations, that’s just fine.

But, that might not be the completely optimal way to configure a VM that is hungry for I/O (such as a large SQL Server), if you have the option to configure it a bit more closely.

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Jan 082014


For those of you with your mission-critical servers already virtualized on a VMware-based virtual infrastructure, are you using the VMware Paravirtual SCSI driver to boost your I/O performance by an average of 12%? I use it for all of my I/O intensive virtual machines, including SQL Server and Oracle VMs, and you should too!

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?

preferences-other-3It’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.

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