Datasheet

Chapter 1: Overview of Virtualization
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cause packet routing and forwarding problems, and it is a difficult problem to identify. (A specific block
of MAC addresses that should be used with Xen is discussed in Chapter 8 .)
In general, the use of virtual network interfaces and virtual machines can make many network
management tasks more complex unless you have spent a significant amount of time considering and
working around potential problems during the planning phase of your virtual machine infrastructure.
Increased Administrative Complexity
Simplified system administration was identified earlier as a potential benefit of virtualization, but this
may not always be the case if you are already using distributed system-management utilities that don ’ t
understand virtual machines. If this is the case, or if you are using multiple virtualization solutions at the
same time, you should make sure that any management utilities that you already depend on (or plan to
purchase) can understand virtual machines, or you ’ ll have to restrict their use to only those systems that
they can communicate with. This may not be a problem, but it ’ s certainly a point to consider.
Identifying Candidates for Virtualization
The goal of most virtualization efforts is to consolidate multiple servers on specific physical hardware
platforms. Although it is tempting to approach the question of where to start by identifying specific
physical machines that you would like to eliminate, a better starting point is to consider the software
that you need to support. Identifying older hardware, machines with unique or aging peripherals and
storage systems, and so on is an excellent second step in your planning process, providing an excellent
mechanism for cross - checking the physical hosts whose software you plan to move to virtual machines,
but it is generally most effective to begin the virtualization planning process by identifying the software
that you need to continue to support and its requirements.
Identifying existing software that can be moved from physical hosts to virtual machines involves a
number of different factors, including hardware requirements, operating system and execution
environment software requirements, the usage pattern of the software, and the load that it will place on
its host system.
Collecting hardware, operating system, and execution environment data is most easily done using a
checklist of some sort to ensure that you collect the same sort of data about all applications and systems
that you are considering for virtualization. A spreadsheet with appropriate columns is typically the most
useful framework for collecting this information, because it enables you to sort by various columns and
identify software with specific physical constraints or current physical host systems that you may be able
to either combine in a single virtual machine or implement in separate virtual machines that are hosted
on a single piece of physical hardware that satisfies the requirements for multiple pieces of software.
The following list shows the information that you should collect for each of the applications that you are
considering moving to a virtual machine. You may actually want to collect this data for all of the
applications that your systems support. This will not only provide a good reference for support and
licensing information, but it may also help you spot applications that are candidates for moving to
virtual machines.
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