With so much hype and buzz in the market surrounding the idea of virtualisation, it’s easy to get caught up in the excitement. For the uninitiated, the differences between Hardware Virtualisation tools like VMware Virtual Infrastructure and those that drive O/S Virtualisation like Parallels Virtuozzo Containers are of little consequence. But in reality their goals and feature sets are vastly different. With all the types of virtualisation products
in the market today, understanding their nuances and ultimately finding those that work best in your environment can be challenging.
Specific to the products that drive Hardware Virtualisation and O/S Virtualisation, these two architectures are designed with different workloads and environments in mind. Some environments, like those with high density or high levels of O/S homogeneity, may work better with one product than with another. Other environments, where widespread O/S support is a high priority, may work better with another. Finding the correct virtualisation tool to solve an organisation’s consolidation needs depends on the needs of the environment combined with the feature sets of the product.
Let’s start by looking at a few of the realities surrounding virtualisation in the IT marketplace today: Gone are the days of asking, “So, what is virtualisation?” Those questions today give way to, “How best do I fit it into my environment?”
One of the most critical components in any virtualisation assessment is an understanding of all the potential architectures as well as how they can fit into the computing
When it comes to virtualisation products and solutions, it’s all about the layer.
As they say in real estate, it’s all about location. With virtualisation, it’s all about the layer. Referring to virtualisation and the products that support and drive virtualisation that “layer” refers to the level within the system at which the virtualisation occurs. Hypervisor-based Hardware Virtualisation (Parallels Virtuozzo Containers) solutions include their layer of processing either atop an existing operating system or—in the case of VMware Virtual Infrastructure—directly on top of the hardware “bare metal”.
This complete isolation and independence between individual virtual machines is at once VMware’s greatest strength and greatest area of management complexity. As virtual machines are effectively segregated units, their management must be done in ways very similar to segregated physical machines. Patching, software management, resource allocation, and security are all horizontally scaled as the number of virtual machines increases. This can lead to a virtual “sprawl” of devices to manage as the environment scales. In effect, by virtualising your environment in this manner, you require the same level of management effort as with physical machines
because each virtual machine is managed individually.
Virtuozzo Containers additionally gains management advantage through server templating. The linkage between the host and its onboard Containers means that any update of files on the host has the ability to directly and immediately impact all residing Containers. Patching the host can immediately patch all the Containers. Adding an application to the host can immediately add that application to all the Containers. Applications destined for individual Containers rather than the host itself can be packaged prior to deployment, further making possible rapid configuration changes. This process of server templating reduces the overall management cost associated with a horizontally- scaled containers virtualisation environment.
One concept you’ll find again and again in server virtualisation is the idea of consolidation. This term defines the number of physical machines you can collocate onto a single virtualisation host, and is a major factor in realising the overall return on your virtualisation expenditure. Depending on the workload requirements you intend to run within your containers virtualisation environment, you’ll find that some architectures have the ability to support much greater numbers of systems—and therefore a higher level of consolidation—than others.
Many virtualisation deployments fail, often due to mismatched technology and needs. Sometimes more than one virtualisation solution may be the best answer.
Due again in some ways to those early attempts at defining virtualisation as a specific product set, some project teams may not look at all possible virtualisation tool sets that fit their needs. When the needs of a computing environment don’t match with the tool sets installed, it grows difficult to fully recognise the greatest return on the virtualisation investment.
Let’s take a focused look now at each of these two virtualisation solutions, where they work the best, and where they may not necessarily be a best fit. Our discussion here will focus on four axes that describe each product’s capabilities related to Density, Efficiency, Scalability, and Manageability.
In the world of virtualisation, one concept that is of major importance to most environments is consolidation.
VMWare – VMware Virtual Infrastructure environments support the stand-up of multiple systems per physical host. The physical host’s hypervisor layer handles the proxying of physical resources to onboard virtual machines that require attention. Each system is an independent entity from the perspective of its files on disk. Because each virtual machine requires its own separate file set, multiple virtual machines will require multiple copies of virtual machine files.
This total independence allows for the complete segregation of virtual machines from each other. It also means that Virtual Infrastructure-based virtual machines cannot share memory, cache, or files on disk between processes across individual virtual machines. Each process running on a virtual machine is handled by the processors on the physical host and is stored within the physical host’s RAM. But the running and caching of activities on one physical machine by definition cannot be shared with other virtual machines on the system. This is good from the perspective of ensuring virtual machine isolation from each other (as is in the case of virtual machines that span security boundaries), but un-optimized from the perspective of resource sharing.
Virtuozzo – Containers within a Virtuozzo environment operate much differently than virtual machines within Virtual Infrastructure based environments. File system buffers and cache within a Virtuozzo-based environment are shared between the host and any onboard Containers. This first means that a single cache can support the needs of all Containers as well as the host, which improves resource use. Since multiple virtual machines do not require their own independent and redundant locations for physical RAM and cache, this tends to reduce the overall need for RAM as well as resource-costly swapping activities. It also means that an application installed onto the host can be used by all residing Containers if desired. Any change in configuration that occurs to the onboard Container is written to the disk using a Copy-on-Write mechanism that ensures the uniqueness of the Containers configuration.
All this leads to the potential for a significantly large total density that can be provided by a Virtuozzo-based environment. Furthermore, because of the high level of resource optimization, this density ratio serves for traditionally highload workloads like email systems and databases.
Both virtualisation solutions are highly efficient in their use of available physical resources.
VMWare – One feature of Hardware Virtualisation architectures is their reliance on emulated driver sets to support the hardware needs of the on-board virtual machines. A limitation of these emulated driver sets is that the process of doing the translation incurs an overhead to physical resources. Doing the translation involves additional work on the part of the host. Because the host needs to perform this work with all onboard virtual machines, it reduces the total amount of physical resources for the virtual machines. More recent computer systems with onboard virtualisation extensions built into their processor chips can alleviate some of this overhead.
Virtuozzo – With O/S Virtualisation architecture and Virtuozzo Containers, the architecture is different. Virtualisation Virtuozzo operates at a layer above the operating system rather than below it. Because all residing virtual machines are components of the host, there is no need for emulated driver sets. The driver sets of the host are the very same as the files for the onboard virtual machines. Lacking this emulated hardware eliminates the overhead of Hardware Virtualisation architectures. It adds the potential of achieving performance near that of the native server itself as well as assignment of physical resources that scale to the full resources of the host server.
Both Virtual Infrastructure and Virtuozzo Containers enable massive horizontal scalability for on-board virtual machines. Some of the mechanisms used by each product to facilitate this performance management are very similar. Both Virtuozzo and Virtual Infrastructure have the ability to adjust physical resources that are assigned to on-board virtual machines.
VMWare – With Virtual Infrastructure, a limitation associated with the Hardware Virtualisation architecture means that only a preconfigured quantity of resources can be assigned to virtual machines.
Virtuozzo - With Virtuozzo, there are no limitations. Any hardware resources available to the host can be made available to the residing virtual machines.
As an example, Virtual Infrastructure has a limitation on the number of processors that can be assigned to an on-board virtual machine. Virtuozzo does not. This results in a highly optimized use of available resources, and therefore the potential for excellent efficiency in resource use. Additionally, manipulating the level of resources with Virtuozzo can be done without an impact to the virtual machine. Doing the same with Virtual Infrastructure often requires a reboot of the virtual machine. This fact enhances the ability to dynamically adjust resources as necessary to support the needs of the environment.
Lastly, no discussion regarding these two architectures is complete without the recognition of the management activities associated with their use.
VMWare – Virtual Infrastructure includes an excellent interface for the centralized management of all virtual machines on all physical hosts within the datacenter. This single, unified interface allows for all virtual machines
to be managed from one place, no matter where they may be hosted or which operating system they run. Intrinsic to the interface are schedulable as well as scriptable interfaces for managing the virtual machines. Coding framework exposure allows for the addition of 3rd party tools for additional management as necessary.
Virtuozzo - Virtuozzo Containers are a management toolset that directly manages the internal configuration of each residing Container. Due to its architecture, it is feasible to consider Virtuozzo as much as a systems management tool as a virtual machine management tool. Virtuozzo supports the creation of application packages that can be installed to any host or Container as necessary through the same management interface that handles Container administration. Containers can similarly be backed up, reconfigured, created and templatized, and have their configurations changed en masse through this same interface. In environments where the management of individual machine configurations is important and desired through the same interface as management of virtual machine configurations, these capabilities can enhance overall manageability.
Above all, when using Virtuozzo Containers as the virtualisation solution, there is only a single operating system to manage. Residing virtual machines with Virtuozzo, though segregated, are components of the host operating system. By not having to manage multiple operating systems, environments with Virtuozzo can focus on supporting their primary O/S without the need for the additional management and maintenance
overhead associated with supporting an additional O/S.
The Final Outcome – DIFFERENT COMPUTING ENVIRONMENTS REQUIRE DIFFERENT VIRTUALISATION SOLUTIONS
In the end, the determination of which works best in your own computing environment is up to you. The most important facet of this determination is the understanding of how each virtualisation concept functions, the features it provides, and where it can provide the best return on your virtualisation investment.