Paravirtualization vs. Full Virtualization: Pros and Cons

Virtualization is now a key part of any IT professional's toolbox. It offers a practical and cost-effective solution for many key IT use cases and, for many businesses, has become a mainstay of how they develop and upgrade their mission-critical applications.

However, full virtualization does have its downsides. It can require significant upfront costs, as well as the potential to create issues with security, availability and scalability. Therefore, many businesses may consider turning to other options for certain use cases where a full virtualization deployment may not be suitable. One common answer to this challenge is paravirtualization.

So what is paravirtualization, when should businesses consider using it, and can it really be a viable alternative to a complex full virtualization solution?

What is paravirtualization?

Virtualization refers to the building of a virtual, as opposed to physical, computing resource. It can be used to run an operating system (OS), server, desktop, storage device, or network. Paravirtualization, meanwhile, is a specific type of virtualization that, while using many of the same concepts as traditional virtualization solutions, differs in how the various components of the tool interact.

In a full virtualization environment, the guest OS is isolated from the virtual machine by the hardware and virtualization layer, so it has no direct interaction with the hypervisor. In paravirtualization, however, the guest OS connects directly to the hypervisor without the use of any other apps or software. Some familiar examples of the paravirtualization approach include VMWare and Xen.

This enables several different operating systems to run on the same set of hardware by effectively sharing resources such as processing power and memory. The intention behind this is to improve performance in order to perform operations that have traditionally proven difficult to achieve in full virtualization.

The benefits of paravirtualization

Among the main benefits provided by paravirtualization is the boost in speed. As the OS is interfacing directly with the hypervisor, with no extra steps in between, this provides a smoother, faster experience.

For an analogy, think of full virtualization as attempting to navigate your way around a foreign country using only a translation app. It works, and you'll get where you need to go, but it can be a slow process as both you and everyone you speak to have to communicate indirectly via the app.

Paravirtualization, on the other hand, is like being able to speak the local language fluently. This removes the need for the middleman (the app) and lets you communicate directly in order to get the information you need. While using a translator is easier, and learning fluency takes a lot of extra effort, the benefits can be worth it in the long run.

In practical terms, this can result in faster software migrations, improved utilization of resources, lower energy costs and simpler backups.

The disadvantages of paravirtualization

If this sounds good, you may be wondering why you wouldn't deploy paravirtualization all the time. However, there are several downsides that come with this technology that can reduce its overall effectiveness. To go back to the translation analogy above, it can be difficult and time-consuming to learn the language to a strong enough degree to be useful, and the gains can vary depending on how often you want to use it, and for what purpose.

For instance, while paravirtualization generally promises significant performance gains, the actual results can vary significantly. Factors that go into this include the workload and the type of application you're running, as well as the hypervisor and OS in use.

To run paravirtualization successfully, you'll need a suitable hypervisor and a modified OS capable of interacting with it through hypercalls. Non-modified OSs may not work with paravirtualization, while the close dependency between the hypervisor and the OS can be broken by OS updates.

As a result, it can be difficult to implement paravirtualization on an enterprise-wide scale due to the inconsistencies in performance and the need for ongoing maintenance.

Security considerations also need to be taken into account. Some security experts suggest that a direct connection between the OS and the hypervisor can expose your network to a wider range of threats, while may also impact your use cases and the type of data it has access to.

When might you use paravirtualization?

Because of these challenges, most organizations treat paravirtualization as a relatively niche solution that should be reserved for a few key scenarios, in which the benefits of the performance advantages outweigh the downsides.

For example, paravirtualization solutions can often be found in use cases such as:

• Disaster recovery solutions
• Data migration between different operating systems
• Capacity management
• Separating testing and development environments

In addition to this, paravirtualization can also be used for maintaining legacy workloads or highly customized applications that remain dependent on older hardware solutions, though this is becoming an increasingly niche scenario as businesses modernize their systems.