With any real deployment of XenServer, you’re going to run into situations where you need to add VCPUs. With server or desktop virtualization, it is commonplace. Unfortunately, at least with older versions of XenCenter/XenServer, it isn’t as simple/easy as it should be.
Here is the process:
go to xencenter, shut down VM. add another VCPU, then do the following…
Get the UUID using the following command:
xe vm-list name-label=
Set the number of cores per processor using the following command
xe vm-param-set platform:cores-per-socket=’4’ uuid=
Set the number of VCPU’s at startup with the following command
xe vm-param-set VCPUs-at-startup='2' uuid=
note: this value may need to be 1 for the first go around with these commands.
Finally, Set the number of max cores with the following command
xe vm-param-set VCPUs-max='4'