Home > Virtualization Concepts > Physical Requirements vs. Virtual Provisioning (Part 2)

Physical Requirements vs. Virtual Provisioning (Part 2)

After a delay, I bring you Part 2 in the discussion of Physical vs Virtual Provisioning. In the opening post of this series, I gave a few recent examples of VM request that had graced my screen and shocked my brain. In today’s post, I want to examine some of the reasons why the requirements differ from a physical to a virtual machine.

The main difference between a physical machine and a virtual machine is the lack of hardware. By lack of hardware, I don’t mean there is no hardware at all; we all know there has to be hardware somewhere. By no hardware, I mean the machine and OS itself aren’t aware they are virtual and don’t run on its own physical server. I don’t want to get too caught up on that discussion. The point to my comment is that the lack of the physical hardware means a lack of physical hardware drivers. We all know how much of a pain, and resource hog, drivers can be. No one really knows how much of your CPU cycles and Memory I/O activities are the work of drivers translating actions between the physical and application level. 

This is one of the HUGE benefits of virtualization with ESX. The OS of the VMs don’t have to spend the time and resources required to translate actions between drivers and the physical devices. In a physical machine, the OS has to allocate resources to perform this task, and these overhead resources create an addition requirement on top of the application and other OS needs. With a virtual machine on an ESX environment, the driver translation takes place on the ESX host’s hypervisor. This allows for less overhead resources to be required, lowering the requirements of a virtual machines resources to perform at the same or better level than its physical counterpart.  This improvement increase ten-fold when you P2V a physically intensive machine, such as an SQL server using FCS. Since a lot of the data retrieval takes place over the HBA to the SAN, this means a lot of resource are used to perform this data retrieval. This is the reason you can see a huge improvement in performance when virtualizing platforms.

This key characteristic in the operation of a physical machine and a virtual machine is really what allows for a major difference in provisioning requirements. I believe it’s also the lack of knowledge on how this operation works and affects resource contention on a physical and virtual machine that creates the problem this series is addressing. Once this knowledge is shared and an understanding of it has achieved, then I think the frequency of over powered VM request will diminish.

In the next part of the series I will look at ways to identify and address underutilized VMs to increase the available capacity on your ESX host.

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