November 28, 2007, 5:26 PM — VMware's virtualization solutions promise greater hardware utilization and
flexibility. Yet, like all virtualization technologies, they carry a certain
amount of risk. Stack too many servers and you achieve significant financial
gain but incur the risk of operational incidents and performance problems in
your production environment. Ignore the business-related aspects of your production
environment that aren't present in the lab and you may put critical apps at
great risk. Rely too heavily on some of the advanced automation features of
VMWare without the proper planning and you could wind up with bigger problems
than those you were trying to solve in the first place.
Proper planning is at the heart of any technology optimization initiative and
this applies to VMWare as well. Large scale virtualization necessitates a data-driven
approach, carefully evaluating elements such as business considerations, technical
constraints, and workload patterns. Things in the VMWare world are very fluid,
so it's not only important to achieve an optimal initial placement of virtual
machines, but also to understand how to keep the environment optimized..
Virtualization planning can be very complex if not using the proper planning
tools, but regardless of the approach, organizations should ensure that they
are following some basic guidelines during the process.
Watch for Technical Factors that May Introduce Risk: Be careful when
combining servers that have differing configurations, diverse underlying platforms,
or varying network/storage connectivity. Combining servers that touch too many
networks onto a single physical host can drive up costs through the increase
of NICs and PCI extenders (blade racks are particularly sensitive to this).
Be sure to uncover any hardware or configurations of interest, such as SAN controllers,
token ring cards, IVRs, proprietary daughterboards, direct-connect printers,
or other items that are not part of the standard build. This process, called
variance analysis, reveals hardware configuration affinities and "outliers",
which ultimately helps avoid any interruption of critical business services
during the virtualization process.
Consider the Key Business Constraints that Govern the Environment: Consider
real-world business constraints, such as availability targets, maintenance windows,
application owners, compliance restrictions, disaster recovery strategies, and
other business sensitivities. Most small-scale virtualization planning doesn't
go beyond simple workload analysis, yet any foray into larger production environments
will show that it is very important to dig much deeper. For example, it's not
unheard of to combine virtualization candidates based solely on utilization
data and end up with a dysfunctional environment where there is not a single
time in the calendar when the physical server can actually be shut down for
maintenance. Considering the maintenance windows of the applications in the
planning phase will avoid such problems, and it is not always wise to rely on
Vmotion to get out of a jam. Likewise, mixing different availability levels
can either create risk or waste expensive hardware.
Tackle the Political and Financial Ramifications of Sharing Infrastructure:
Another issue to consider is the politics of these consolidation decisions.
Application owners may have real or perceived reasons why they cannot share
infrastructure and these often translate into additional constraints and/or
what-if analysis in order to resolve the issues. In addition, most chargeback
models aren't sophisticated enough to deal with virtualized infrastructure and
will break down if resource sharing crosses certain boundaries. Using affinity
regions based on departments and application owners may be a wise decision in
cases where political or financial considerations pose a challenge.
