Is it safe to allocate logical CPUs to a VM after creation

Question

We're going to be serving our portal software on a virtual machine running Centos 5.2 on VMWare ESXi.

We're initially going to allocate two logical CPUs but there's a possibility that we might want to add an additional two some time in the future. We don't want to allocate all resources at this time because a few VMs are fighting for space on the server.

If we decided to move our VM off to a separate server later on and allocate additional logical CPUs bringing it to four, will this cause us any problems?

Answer 1

Yes you can do this. You can change the number of CPUs like you can change the amount of RAM the VM sees. You should shut down your VM, then change the number of CPUs, then power on the VM. Whether or not the guest OS handles the change smoothly is up to that OS, something as new as Centos 5.x should do just fine.

If you're using SMP VMs, you should read: http://communities.vmware.com/docs/DOC-4960 for more information. Generally a single VM shouldn't have as many virtual CPUs as your host has CPU cores.