Databases Reference
In-Depth Information
Each virtual server believes and appears to be running on a traditional physical server, with full
access to all of the CPU, memory, and storage resources allocated to it by the system administrator.
More importantly, in order for virtualization technology to work, the virtual server's operating
system software can use the same hardware registers and calls, and memory address space,
which it would use if it were running on a dedicated physical server. This allows software to run
on a virtual, rather than physical, server without being recompiled for a different type of hardware
architecture.
Cloud Computing
It's almost impossible to read technology news these days without seeing references to cloud
computing, and more commonly private clouds and public clouds. One of the advantages of
cloud computing is that new servers can be deployed very quickly, literally in just minutes, and to do
this they use platform virtualization. While this chapter won't go into how cloud computing works,
it's worth remembering that at the technology layer, virtualization is a key enabler of this
technology revolution.
Private Clouds
In summary, private clouds are usually a large and centrally managed virtualization environment
deployed on-premise, typically in your data center. The virtualization management software they
use often has management features added that allow end users to provision their own new servers
through web portals, and for the dynamic allocation of resources between virtual servers. A key
benei t for businesses too is the ability to deploy usage-based charging models that allow individual
business departments or users to be charged for their actual usage of a virtual server, as well as
allowing more self-service administration of server infrastructures.
Public Clouds
Public clouds, more often referred to as just cloud computing, are very similar to private clouds but
are hosted in an Internet connected data center that is owned and managed by a service provider
rather than an internal IT department. They allow users from anywhere in the world to deploy
servers or services, through non-technical interfaces such as a web portal, with no regard for the
underlying physical hardware needed to provide them. Microsoft's Windows Azure service is an
example of a cloud computing service.
WHY VIRTUALIZE A SERVER?
“Why would you want to virtualize a server?” is a question I surprisingly still hear, particularly
from people with no experience of having used virtualization technology. A typical follow-on
comment is often “I've heard you can't virtualize database servers.”
A few years ago, that question and comment were probably worth asking when IT teams were
discussing virtualization of servers running SQL Server. SQL Server is a resource hungry application
that needs particularly large amounts of memory and fast storage to process big workloads, and
a few years ago, virtualization technology sometimes struggled to deliver those resources. As an
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