Databases Reference
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physical server, but still give each its own operating system environment to use. Consequently, server
hardware expenditure decreases, but also equally and perhaps more importantly, so do power,
cooling, and space costs.
Another technical benei t comes from how virtual servers are allocated resources, such as memory
and CPU. In the virtual world, providing sufi cient physical server resources are available, creating
a new virtual server is purely a software operation. When someone wants a new server deployed, no
one would need to install any physical memory, storage, or CPU hardware, let alone a completely
new physical server.
Likewise, an existing virtual server can have additional resources such as extra CPUs or memory
allocated to it at the click of a mouse — providing the physical host server has the capacity—then
the next time the virtual server reboots it will see and be able to use the additional resources.
Both deploying a new virtual server and allocating addition resources can be done in seconds,
drastically increasing the l exibility of the server environment to react to planned and un-planned
workloads.
Encapsulation
The i nal technical advantage we'll discuss is a benei t of something virtualization does called
encapsulation.
Despite how they appear to the operating system and applications running within
the virtual server, when virtual servers are created, their data is stored as a set of l at i les held on a
i le system; therefore, it can be said that the virtual server is “encapsulated” into a small set of i les.
By storing these l at i les on shared storage, such as a SAN, the virtual servers can be “run” by any
physical server that has access to the storage. This increases the level of availability in a virtual
environment, as the virtual servers in it do not depend on the availability of a specii c physical server
in order to be used.
This is one of the biggest post-consolidation benei ts of virtualization for IT teams because it
enables proactive features to protect against server hardware failure, regardless of what level of high
availability support the virtual server's operating system or application has; more about these are
discussed in the Virtualization Concepts section. This type of feature won't usually protect against
an operating system or database server crashing, but it can react to the physical server the virtual
server was running on un-expectedly going ofl ine.
This level of protection does incur some downtime however, as the virtual server needs to be
restarted to be brought back online. For those looking for higher levels of protection, VMware's
Fault Tolerance feature lock-steps the CPU activity between a virtual server and a replica of it; every
CPU instruction that happens on one virtual server happens on the other.
The features don't stop there. Some server virtualization software allows virtual servers to be
migrated from one physical server to another without even taking them ofl ine, which is known
as online migration and is covered in the “Virtualization Concepts” section of this chapter. This
feature can be critical to reducing the impact of planned downtime for a physical server as well,
whether it is for relocation, upgrading, etc.
There are, as you'd expect, limitations to how this can be used, but generally it's a very popular fea-
ture with system administrators. The “Extended Features of Virtualization” section of this chapter
discusses more about these features.
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