Virtualization is one of the hottest trends, especially
to combat server sprawl and increase operational
efficiencies, and it can reduce TCO. However, database
workloads like SQL Server can be some of the most
troublesome to virtualize. Here are commonly asked questions
about virtualizing SQL Server.
Is virtualization the only way to consolidate servers?
Although virtualization is one of the best ways to perform
server consolidation, it’s not the only way. For instance,
you can consolidate database servers simply by adding
additional databases and their workloads onto a single
server. In addition, you can run multiple instances of SQL
Server on the same system. These are examples of how to
consolidate your workload without virtualization.
How does virtualization help with server consolidation and
operations in general?
First, because virtualization technology abstracts the
server or OS layer from the underlying hardware, it’s easier
to move a server to different hardware for better scalability
or for disaster recovery. Next, not all workloads or
applications are compatible with one another and server
consolidation using virtualization enables you to keep all
your databases on completely separate servers each running
under their own OS.
How much overhead does virtualization impose?
The actual overhead depends primarily on the virtualization
infrastructure and the I/O characteristics of the workload
that’s running. However, a general rule of thumb is to
expect a 10 to 15 percent reduction in performance between
a physical machine and a virtual machine (VM). Obviously,
if you’re running in a server consolidation environment,
other active VMs will make an impact on overhead, too.
What types of SQL Server implementations are best suited
to virtualization?
Because virtualization adds overhead, the raw performance
of a VM won’t match that of a physical implementation.
Virtualize smaller or departmental SQL Server workloads
where there is excess CPU and I/O capacity. Be wary of
virtualizing database workloads that have high resource
requirements. However, many enterprise databases can be
virtualized and still meet their service level agreements. It
just takes more planning.
Does virtualization make SQL Server administration
harder or easier?
Virtualization is not a panacea for server administration.
Although they’re on a common hardware platform, each
virtual server still has the same management requirements
as a physical server—services need to be started
and stopped, queries need to be tuned, databases need
to be backed up. You can still use management tools
such as Enterprise Manager and SQL Server Management
Studio just as you would to manage a standard
physical server.
SQL Server is licensed per processor—how does that
work if you’re running multiple SQL Server VMs on an
8-way host?
Microsoft licenses SQL Server per virtual CPU, not by
the number of host CPUs. If you have a SQL Server
VM that uses one virtual CPU and the VM runs on an
8-way host, then you only need one CPU license for SQL
Server. Microsoft allows an unlimited number of virtual
instances for SQL Server 2005 Enterprise Edition, with no
additional licensing costs.
End of Article
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