Practical Cloud Knowledge: Install, Configure, and Manage - Deploying and Managing a Cloud Infrastructure - page 218

This includes the operating system, all the applications, and data in the physical machine.
Sometimes it is just the data that needs to be migrated to a virtual machine, so the process
only needs some form of replication or copying. But if a whole physical machine needs to
be converted to a virtual machine, special software is required. The tools are often pro-
vided by the service provider.
Virtual to Virtual (V2V) Virtual to virtual migration is often done when a host needs to
be shut down for some reason, such as maintenance or retirement. The virtual machines are
often cloned and then deployed to the new host while the original virtual machines are still
running on the old host so that there will be little to no disruption of services.
Virtual to Physical (V2P) This is the opposite of P2V and is often done when a virtual
machine server needs to be able to produce more power in order to serve better. That is the
current limitation of virtual machines; they cannot scale too much vertically, only horizon-
tally. So when raw power is required, the best option is to convert the virtual machine into
an actual physical server so all the applications and data have to be migrated there. The
tools and procedures on how to convert a virtual machine into a physical one is provided
by the service provider.
Maintenance Scheduling Maintenance is important for any system because it ensures
that the system will be performing in top condition for the duration of its lifetime. But it
also means that there will be possible disruptions as the system itself or at least parts of it
are taken down so that maintenance can be done. This will have an effect on the system's
performance, making it slow and run at reduced capacity because of the missing parts.
Because of this possible disruption, the maintenance schedule has to be set accordingly,
and it has to be performed within the shortest time possible.
Reasons for Maintenance The main reason for maintenance is to keep the system running
at top condition and to prevent possible downtime and errors from happening in the future.
But maintenance is not only about keeping everything together; upgrades, new feature
releases, and testing all count under maintenance.
Virtual Network Components The cloud environment is defined by its virtual compo-
nents, all of which are logical representations of physical devices and constructs. These
components are the virtual CPU, virtual disk, virtual NIC, virtual switch and router,
virtual memory, virtual HBA, and many more.
Shared Memory Shared memory by definition is a pool of memory that can be allocated
to any client that needs it. Unfortunately, in current implementations it is not yet possible
to literally share this resource into a pool so all guest operating systems would still get their
much-needed memory from the host machine.
Virtual CPU The virtual CPU is the logical counterpart of the physical CPU, and rather
than being able to directly control the host's CPU, this virtual CPU is simply a representa-
tion of timeshares that are allocated to it from the host's overall CPU time by the hypervisor.
Together with graphics processing, this is the biggest unscalable factor for virtual machines.
When more power is required by a virtual server and the problem cannot be remedied by