Hardware Management - Deploying and Managing a Cloud Infrastructure - page 223

more control, and they are able to feel more at home as well as get all of the benefits that
cloud computing offers.
To date, only ProfitBricks, a relative newcomer to the cloud scene, has announced explicit
user-end BIOS configuration support. The larger providers like Amazon, Microsoft, Oracle,
and Google do not explicitly allow (as a feature) users to directly configure BIOS settings for
the infrastructure or for individual VMs, but they may support this through other methods,
such as special configuration requests, internal script programs, and other specialized tools.
Minimum Memory Capacity and Configuration
Virtual machines may not really be as fast as their equivalent hardware with the same specs,
but numbers are still important. When you're creating virtual machines, the minimum mem-
ory capacity should be above that of the requirements of the OS and the required applications
combined. In a cloud environment, you can provision for additional resources, but, for exam-
ple, provisioning for additional resources like memory to hundreds or thousands of virtual
machines because of miscalculation of memory requirements would become a costly mistake.
This doesn't mean that virtual machines are inefficient; on the contrary, they are cost
effective in terms of the ratio of computing power to cost. The message here is that too
much of something won't necessarily make things better. After a certain point, you will
usually get diminishing returns, especially in a service environment where every move costs
money. You really need to plan every move so that you reap the actual benefits instead of
additional costs.
Number of CPUs
Depending on the function of a virtual machine, whether it is meant to be a server or a
simple personal computer, the number of required virtual CPUs (vCPUs) will differ. The
number of vCPUs will depend on the number of logical cores on the host machine and
the type of guest operating system (non-server OSs will be able to support fewer CPUs)
installed on the virtual machine. The number of logical cores is double that of physical
cores installed if hyperthreading is enabled. But this will entirely be up to the provider if
its platform can support the number of CPUs that your virtual machines require. It also
requires support for virtual symmetric multiprocessing (SMP) on the guest operating sys-
tem. Figure 8.1 shows how virtual SMP factors into the virtualized environment.
Since vCPUs are simply representations of time slices in the host's physical and logical
CPUs, a virtual machine cannot have more virtual CPUs than the number of logical cores
that the host has. Again, this really depends on the maximum number of vCPUs that your
provider can license to you. For example, VMware vSphere imposes the following limits
per license:
Standard A maximum of eight vCPUs and 24 GB of memory per VM
Enterprise Eight vCPUs and 32 GB of memory per VM
Enterprise Plus 32 vCPUs and 48 GB of memory per VM