An Introduction to OS Virtualization and Virtuozzo
How is Virtuozzo different?
Hardware virtualization is well-known in the server virtualization market. OS-level virtualization expands
the opportunities for server virtualization and is a complementary or replacement technology in many
How does Virtuozzo compare to hardware virtualization technologies such as VMware, Xen, Virtual
Server and Parallels?
Hardware virtualization solutions all have the same premise: resource consolidation. The end goal of the
consolidation is to be able to place many different and separate operating systems on the same server.
Each of these technologies, whether it is a hypervisor or an OS, has an underlying piece of software that
is the basis of the relationship between the hardware and the residing software. Above the hypervisor or
virtual machine monitor level is the virtualized hardware level. In order to assign resources, this type of
technology must virtualize every single piece of hardware, in essence recreating the work of the hard-
ware vendors and the OS software vendors that already support the hardware. Finally, inside the guest
virtual machines, there is a complete copy of an additional operating system and the residing workloads
Hardware virtualization has its benefits. At least on the leading market solution, just about any operating
system is supported. It is possible to load Windows next Linux next to Solaris, and it still supports older
OSs. Despite the benefits, the flexibility of this type of solution comes with a lot of overhead and inef-
Many organizations find that after deploying a hardware virtualization solution, they loaded an entire
server with virtual machines all running the same operating system. This happens for a variety of rea-
sons, mainly because most organizations have enough servers to consolidate like operating systems and
the system administrator supporting the server has the skill set of that OS. Suddenly, that goal of loading
any operating system on a single server doesn t warrant the associated overhead of this type of flexibility.
Further limitations inherent to hardware virtualization lead to additional overheads and inefficiencies, as
addressed in the following points:
" A single application has two OSs to traverse; the guest-level OS and the hypervisor or host OS.
More processing equates to slower responses and more overhead.
" Each OS takes space in memory, and memory is always the most constrained resource on a server.
While some vendors have taken steps to maximize memory usage, the inefficiencies still exist.
" The duplicate OSs consume hard drive space and must be licensed and managed separately. Be-
cause virtual machines don t need hardware justification, many IT organizations are now starting to
see OS sprawl instead of server sprawl.
" Hardware support and interoperability for all of the hardware on the market is difficult to emulate well,
so it is often a source of slower response times and higher processing overhead.
As an OS-level virtualization solution, Virtuozzo uses a single standard Operating System on a server.
Not only does this model eliminate the inefficiencies of hardware virtualization, but there are advantages
inherent to this approach:
" Virtuozzo uses all of the real hardware and OS software. There are no rewritten drivers or OS
technology. There is also very little or no delay in supporting new technologies and it performs at
near-native server levels.
" There is no duplicate OS, so it again performs very efficiently.
" Because of the near native server performance, Virtuozzo is used to virtualize high I/O applica-
tions such as data bases and email servers.
" The flexible design allows any VE to seamlessly scale to the resources of the entire server.