Hardware Management - Deploying and Managing a Cloud Infrastructure - page 224

FIGURE 8.1 Virtual environment with SMP

App App App App

Guest OS Guest OS Guest OS Guest OS

vCPU vCPU

vCPU vCPU vCPU vCPU vCPU vCPU

vCPU vCPU

Virtual SMP

Hypervisor

CPU CPU CPU Hardware CPU CPU CPU

This actually means that you may have to purchase additional licenses if you require
more memory per VM, but a maximum of 64 vCPUs seems to be the current technical
limitation for ESX 5.5 hypervisor. Sun VirtualBox 3.0 supports up to 32 vCPUs per VM,
while the relatively new Microsoft Hyper-V still only supports a maximum of 4.
Because of performance and service tiers, you must consider the needs of your organiza-
tion, which will be reflected by the specs of your virtual machines. It's okay to start small as
long as it is enough for your workloads. Cloud flexibility and scalability will always allow
you to grow with your needs. Most providers offer auto-provisioning , which allows you to
scale resources automatically according to load.

Number of Cores

Multicore virtual CPU support allows you to control the number of cores per virtual CPU
or virtual socket in a virtual machine. This is quite useful because not all guest operating
systems support multiple sockets or vCPUs, so using multicore vCPUs can allow a vir-
tual machine to utilize more of the host's CPU cores and increase overall virtual machine
performance.
Again, a virtual machine cannot have more virtual CPUs than the number of logical
CPUs in the host, which is simply the number of physical CPU cores present, or twice that
if hyperthreading is enabled. So if a host has 8 CPUs with four cores each, then it has 32
logical CPUs without hyperthreading and 64 logical CPUs if hyperthreading is enabled.