Posted by Joe Rebis on 10 February 2012 07:06 AM
What does the CPU Priority feature mean when creating a new machine?
The amount of processing power allocated to your virtual machine is calculated by the following equation.
CPU Cores x CPU Priority = Total GHz
The amount of CPU resource a VM is given is the CPU priority (you can think of this as its “share percentage”) multiplied by the number of cores allocated to that VM. This is a minimum number – clients can burst over it, up to 100% multiplied by the number of cores. For example, on a hypervisor with 3GHz CPU cores:
• 100% x 1 core = 3GHz (burstable to 3GHz)
By default, we allow the burstbility of cloud resources for general flexibilty of all of our customers. For example, users are able to create 5 VMs with 100% CPU priority/1 CPU core on a hypervisor with a 4-core CPU. In this example, we would reduce the guaranteed CPU for each VM.
How come I can build a machine with 1 CPU and 1% priority and it works fine?
Since we allow the CPU to burst over it's allocated amount a VM with only 1% priority would still function fine. However, please keep in mind in a crunch, VMs with 100% CPU priority will take precedence over a lower "priority" VM (e.g. 1%) and may not continue to perform as expected- rather than being migrated to a new Hypervisor (HV a.k.a. Host Server) with more resources. This is why this is called "priority" rather than CPU Percentage.
Can I save money with using the CPU Priority Setting?
Yes, we allocate approximately $ .02 cents an hour per 100% priority. So, a VM with 50% priority would mean .01 cents an hour saving about $3.65 per month at the time this article was written. Please see our cloud pricing on the front of our website for current pricing.