Virtual CPUs in vSphere 5

[vinay1]

Hi Techies,

Kindly assist for the below queries?

as per vmware's Configuration Maximums for vSphere 5.0

Number of Virtual CPUs per host = 2048

Number of Virtual CPUs per Core = 25

As for as i understood, One Virtual CPU = 1 CPU core, a bit confusion here, How 25 Virtual CPUs will be created per Core.

[a_p_]

The 25 Virtual CPUs per Core is the maximum supported consolidation ratio. It means that the scheduler may run 25 virtual machines with 1 vCPU each can run on one physical core. However whether this ratio can be achieved or not depends on the workload of the VMs.

André

[weinstein5]

To add a vCPU does run on a single core at a time but a core can have multiple vCPUs running on it - 

[vinay1]

Thanks a lot André for your suggestion, let me confirm, is it like, one vCPU created on a single Core CPU and that vCPU can run a maximum of 25 VMs at a time and there would be no be no CPU contention. if i am wrong, kindly assist further..

[Dave_Mishchenko]

vinay879 wrote:

Thanks a lot André for your suggestion, let me confirm, is it like, one vCPU created on a single Core CPU and that vCPU can run a maximum of 25 VMs at a time and there would be no be no CPU contention. if i am wrong, kindly assist further..

That's not quite it.   When you create a virtual machine, it requires at least one vCPU.  The maximum supported count for a single CPU core is 25 vCPUs, but to get that many running you would need very idle VMs.  Say your CPU core runs at 3 GHz then 25 vCPUs would get about 120 MHz each.  If you have several busy VMs then you could easily max out the CPU core.

You should also note that a vCPU is not tied to a particular physical core.  The CPU scheduler in ESXi may move a vCPU between physical cores depending on the load of the host.

[vinay1]

Thanks Dave, Now its clear to me...:)