IBM Support

Relationship between VCPU and PCPU when creating a Server in a project

Question & Answer


Question

What is the meaning of Virtual and Physical CPU ? That is, in the SimpleSRM while creating a project, in the Server details section, if you are going to create for example a 4 core VCPU VM, then how to adjust the physical CPU?

Answer

The general rules are the following:

- VMware: The value for Virtual CPU must be 1, 2 or 4.
- KVM: Physical CPU cannot be modified.
- Virtual CPU >= Physical CPU

Specifically:

- if you have a request for 3 CPUs then you need to specify 3 VCPU and at least 0.3 physical CPU
- if you have a request for 4 CPUs then you need to specify 4 VCPU and at least 0.4 physical CPU
- if you have a request for more than 4 CPUs, you can deliver it but the amount of VCPU allocatable depends on the VMware version used: if the Vmware version supports till 4 CPUs then the user can use a maximum of 4 CPUs. For 8 CPUs supported version you can use a maximum of 8 CPUs.

Let's say that by default TSAM uses 1/10 of CPU - for example for 1 VCPU it takes 0.1 PCPU. Anyway, if to assign 0.1 PCPU is fine for ESX, for LPAR/PSeries 0.1 PCPU can be not enough, it means that the LPAR will get created but it may stuck at booting time. It depends on the application that you want to run on the LPAR: based on the application size/load, you need to set the PCPU. Just for provisioning purposes you can select 0.3 PCPU for 3 VCPU.

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Document Information

More support for:
Tivoli Service Automation Manager

Software version:
7.2.2, 7.2.3, 7.2.4

Operating system(s):
Windows, AIX, Linux

Document number:
221925

Modified date:
17 June 2018

UID

swg21627754