What is a VMware vCPU

2012-04-12T13:52:00.001-07:00

So a client asked one day on the phone exactly what a vCPU was.
Straight away I knew what it was, but how to explain it in simpleton terms for the client as they were not that tech savvy.

So what is vCPU ?
vCPU is basically a Virtual Central Processing Unit which is assigned to a Virtual Machine (VM) within the vmware ESX infrastructure.
Each vCPU is presented as a single physical CPU core to the VMs operating system. If the host machine (this is the actual physical machine be under a table, or in a rack in the data center) has multiple CPU cores at its disposal, than the vCPU is actually made up of a number of time slots across all of the available cores, in return allowing multiple VMs to be hosted on a smaller number of physical cores.

What is the equivalent of 1vCPU in physical CPU terms?
Genrally 1 vCPU = 1 Physical CPU Core, or a pCPU. However this isnt 100% correct, as a vCPU is made up of time slots across all available physical cores, so generally 1vCPU is considered more powerful than a single core, especially if the physical CPUs have 6-8 cores.

VMware is designed to allow each VM to use a certain proportion of a cores clock time using complex sharing algorithms in its “CPU Scheduler”.
If there is not enough CPU resource to go around say if all VMs are running CPUs at 100% (which is very highly unlikely) then the VMs are automatically migrated using DRS and vMotion onto another host server which has spare CPU resources.

The one thing to remember when explaining to a client is the basics, but to throw out the old idea of how the CPU really works.
A physical socket CPU (pCPU) can contain up to 8 cores. These cores are presented to the VMs as a vCPU.
Additionally due to the fact that VMware has sophisticated algorithms, the vCPU is not just contained to that certain core on a physical CPU should it be overworked and will use any time slots available.
In a dual quad core system giving 8 cores available at one time, that is a lot of time slots to have at hand.

Finally the beginning of many posts (hopefully)

2011-09-13T14:28:00.000-07:00

I don't know how many times I say this, but I do promise to keep up with' blogging'. However after about a day I often wonder why I should bother. Its not like many people would want to know what I do or how I am or anything. Or maybe there is?
I find that I do have to sit down and actually blog, whereas the likes of twitter are just simple mindless updates to the world of what you are doing.
I think this time I will try my best, even if its just updates with cats!!

Oh look:

Chat you guys soon hopefully

RambleBlog

What is a VMware vCPU

Finally the beginning of many posts (hopefully)