Databases Reference
In-Depth Information
Limitations of Virtualization
Like all technologies, virtualization has limits, restrictions, and reasons not to use it in certain
situations. Some virtualization vendors would like you to virtualize every server you have, and in
fact, some now even claim that today that's possible. However, this all-virtual utopia is likely to be
challenged by your applications, IT team, and budget.
Why might you not virtualize a new or existing server? The original reason people didn't virtualize
has rapidly disappeared in recent years: a perceived lack of support from application vendors. In
hindsight, I attribute lack of adoption more to a fear of not knowing what effect virtualization
might have on their systems, rather than repeatable technical issues caused by it. The only actual
problems I've heard of are related to Java-based applications, but fortunately they seem rare and
SQL Server doesn't use Java.
Another rapidly disappearing reason for restricting the reach of virtualization is the resource
allocation limitations that hypervisors put on a virtual server. Despite VMware's technology
supporting a virtual server with as many as 8 virtual CPUs and as much as 255GB of memory as far
back as 2009, most people weren't aware of this and assumed virtual servers were still restricted to
using far less than their production servers needed. As a result, it was domain controllers, i le
servers, and other low-memory footprint workloads that were usually virtualized in the early phases
of adoption.
Today, the capabilities of virtualization software has increased considerably; VMware's software and
Windows Server 2012 now support 32 virtual CPUs and 1TB of memory, per virtual server! This
means even the most demanding workloads can be considered for virtualization. The only current
exceptions are what are considered to be “real time” workloads — that is, applications that process
or control data from an external source that expects reactions or outputs within a specii c number of
milliseconds rather than a certain number of CPU clock cycles. To do this normally, the application
requires constant access to CPU resources, which is something that virtualization software by default
removes. You can enable support for real-time workloads in some virtualization software but doing
so removes some of the management l exibility and resource utilization benei ts virtualization has.
COMMON VIRTUALIZATION PRODUCTS
If you search for virtualization products using your favorite search engine, you'll get dozens of
results for different products, and many opinions about which is best. While it's true that the
virtualization marketplace is crowded, there are still only a handful of vendors that offer production-
ready server virtualization products. Developers, testers, and DBAs may already be familiar with a
wider range of virtualization products, such as Oracle's Virtual Box and VMware Workstation, but
VMware and increasingly Microsoft have the lion's share of the virtualized data center marketplace.
This section looks at the primary server virtualization products available, and some of the
virtualization support that hardware vendors have built into their products in recent years.
VMware
Regardless of what any other virtualization vendor's marketing department may tell you, in my
experience more businesses currently use VMware for their server virtualization platforms than
any other. In my view, the main reason for this is because for a long time, VMware was almost the
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