Databases Reference
In-Depth Information
Virtual Server (or Guest Server or Virtual Machine)
The running of
virtual servers
, also called
guest servers
or
virtual machines
, is the sole purpose of a
virtual environment. Each virtual server has very similar properties to a traditional physical server
in that it will have a number of virtual CPUs, an amount of memory, and a quantity of virtual hard
drives assigned to it. “Inside” the guest server, a regular operating system such as Windows Server
2008 will be installed on drive C: — just like a physical server would. Figure 17-3 shows a diagram
representing the relationship between the hypervisor and the guest servers.
Virtual
Server
Virtual
Server
Virtual
Server
Virtual
Server
Virtual
Server
Virtual
Server
Virtual
Server
Virtual
Server
Virtual
Server
Virtual
Server
Hypervisor Manager
Windows Server 2008
R2
Hyper-V
Hypervisor
Hypervisor
Hypervisor
Hypervisor
Host Server
Host Server
Host Server
Host Server
FIGURE 17-3
Inside virtual servers the hypervisor normally has a set of tools installed, often called client, or
integration, services. These provide a level of integration between the virtual server and its hypervisor
that wouldn't otherwise be possible, such as sharing i les between hypervisor and client or perhaps
synchronizing the system time with the host server.
However, also installed is a driver that, on command from the hypervisor, can begin consuming spe-
cii c quantities of memory within the virtual server. We discuss more about these in the “Demand-
Based Memory Allocation” section of this chapter but for now it's sufi cient to say its purpose is to
be allocated memory within the virtual server so some of the physical memory the virtual server was
previously using can be re-allocated by stealth to another virtual server.
It's called a balloon driver because it inl ates as needed to consume memory within the virtual
server's operating system. Its purpose is not to actually use the memory but to set it aside to ensure
that nothing else within the virtual server is using it.
In comparison with the virtualization software and technology, there's very little to say about
virtual servers, and that's a good thing, as the idea of virtualization is to make the fact they're not
running on a physical server invisible to them.
While virtual servers can be coni gured to “run” on different physical host servers using technologies
like online migration that we'll cover in the next section, at any point in time, a running virtual
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