Full Virtualization vs Paravirtualization

Virtualization enhances the efficiency of IT resources by allowing multiple virtual versions of physical hardware to run on a single server. Instead of dedicating an entire system to one server, virtualization enables the creation of multiple virtual machines (VMs) on the same hardware. Each VM operates as an independent system, which maximizes hardware utilization and simplifies the management of computing environments.

When exploring virtualization technology, it is important to understand key concepts, techniques, and classifications. Two common approaches are “full virtualization” and “paravirtualization.” Full virtualization emulates complete hardware functionality, enabling unmodified operating systems to run seamlessly on virtual machines. In contrast, paravirtualization requires modifications to the operating system to enhance performance and resource efficiency. Each method offers distinct benefits in terms of system compatibility and optimization, depending on specific use cases.

What is Full Virtualization?

Full virtualization is a virtualization technique that completely simulates the underlying hardware in a virtual machine (VM). The VM is fully isolated from the host system, simulating the hardware environment to run an unmodified guest operating system (OS).

How Full Virtualization Works

Full virtualization establishes a virtual environment that emulates the physical hardware of a computer system. Unlike other virtualization methods, it does not require modifications to the operating system (OS) to create virtual machines (VMs) or manage resources. This allows guest operating systems to function as though they have exclusive control over critical resources such as the CPU, memory, and storage. The result is a virtualization solution that provides robust performance and strong isolation for security.

Many hypervisors rely on full virtualization as their foundational approach. This method combines binary translation and direct execution to operate efficiently. Nonsensitive instructions are executed directly by the physical CPU at native speed, without any need for alteration. At the same time, operating system instructions are dynamically translated and cached for future execution. This dual approach ensures that user-level instructions also run at full native speed, maintaining optimal system performance.

Advantages of Full Virtualization

Full virtualization enables admins to run unmodified guest operating systems as the virtual machine emulates the hardware environment. This is crucial for operating systems like those in the Windows family, which are closed-source and can not be modified easily.

Full virtualization enhances isolation and security for VMs because it creates separation between VM environments. It simplifies migration and portability of systems because the same guest OS instance can run on both virtualized and native hardware. Besides, VMs provide backup capabilities through system imaging, which takes only minutes. This allows administrators to capture the entire VM state, including the operating system, applications, and configurations. In virtualized environments, recovery takes only a few minutes.

Disadvantages of Full Virtualization

Full virtualization involves performance limitations since it requires the hypervisor to completely emulate hardware, which demands more processing resources from the hypervisor. Let’s make it clear:

• Full virtualization requires the hypervisor to emulate hardware completely, which can be resource-intensive. This leads to performance overhead when compared to running an operating system directly on physical hardware.
• The hypervisor must translate instructions between the guest operating system and the host hardware, which consumes additional CPU cycles.
• I/O operations in a fully virtualized environment often require multiple layers of abstraction, which can reduce performance and speed compared to native hardware operations.
• Besides, since multiple VMs share resources of the host system, such as CPU, memory, and storage, high resource demand from one VM can have an impact on the performance of others.

In the early days of virtualization, full virtualization saw performance problems due to the considerable emulation overhead. However, with the launch of hardware-assisted virtualization (Intel VT-x and AMD V), full virtualization has been improved with hardware assistance.

Are you looking for virtual machines? We offer virtual machines which are pretty inexpensive with great price-to-performance ratio. To utilize our virtual servers, you can view virtual machine pricing and easily buy a VM (Virtual Machine) which is provisioned instantly.

Examples of Full Virtualization

KVM (Kernel-based Virtual Machine) is a free and open-source full virtualization solution for Linux on x86 hardware that uses hardware-assisted virtualization technologies such as Intel VT-x or AMD-V. It consists of two modules: a loadable kernel module that provides the core virtualization architecture, and a processor-specific module. KVM enables admins to run multiple VMs running unmodified Linux or Windows images. KVM is often combined with QEMU to improve its emulation capabilities.

Besides KVM, VMware is built on the concept of full virtualization. VMware is a leading virtualization technology company that implements full virtualization across different computing environments. In the desktop setting, VMware utilizes Type II hypervisors, which run on top of a host operating system. Or in the server environment, VMware uses Type I hypervisors that run directly on the hardware. Some of VMware’s products are VMware Workstation, VMware Fusion, and VMware ESXi. VMware can perform full virtualization and it also supports paravirtualization.

What is Paravirtualization?

Paravirtualization is a virtualization technique that involves modifying the guest OS. It provides a software interface to virtual machines that is very similar to, but not identical to, the underlying hardware. The guest operating system is aware of the presence of a hypervisor. The guest OS can communicate directly with that hypervisor and commands sent from the guest OS to the hypervisor are known as “hypercalls”.

How Paravirtualization Works

Unlike full virtualization, paravirtualization requires modifications to the guest OS. This modified interface intends to minimize the time the guest operating system spends executing operations that are more difficult to run in a virtualized environment compared to a native, non-virtualized environment. Hence, paravirtualization achieves better performance.

In paravirtualization, the guest OS is aware that it is running in a virtual environment. Paravirtualization allows for direct communication between the guest OS and the hypervisor. The guest OS uses “hypercalls” to communicate with the hypervisor. A hypercall works the same way as a system call, which is used to request services from the OS and provide the interface between the application or process and the OS, except the hypervisor is used. The hypervisor responds to the hypercall by carrying out the specified task on behalf of the guest OS.

Advantages of Paravirtualization

Paravirtualization eliminates the need for full hardware emulation, providing faster execution of tasks and better performance. With paravirtualization, the VMs access system resources directly through interfaces similar to the underlying hardware. Paravirtualization enables direct communication between the guest OS and the hypervisor, which boosts overall performance.

Paravirtualization utilizes the existing drivers in the guest operating system. As a result, it eliminates the need for ​​device driver implementations, then organizations can make use of the hardware in the server. Paravirtualization also improves backup operations and speeds up virtual machine migrations across hosts.

Disadvantages of Paravirtualization

Paravirtualization requires the guest OS to be modified to communicate directly with the hypervisor through hypercalls. Because not all operating systems can be modified, the number of OS options available for paravirtualization is limited. This is especially true for closed-source systems.

In addition, the direct communication requirement through hypercalls creates a close dependency between the OS and hypervisor. Any changes or updates could lead to compatibility difficulties, potentially breaking the virtualization. There are other opportunities for misconfigurations or vulnerabilities.

Besides, the VMs are not as isolated from each other, which could increase security risks.

Examples of Paravirtualization

Xen is the most popular example of paravirtualization. Xen requires the guest operating systems to be modified to support the Xen operating environment. Xen can use more efficient interfaces like virtual block devices and virtual network interfaces to emulate devices. Today, Xen has been extended to be compatible with full virtualization which relies on hardware-assisted virtualization.

VirtualBox is another paravirtualization example. Oracle VM VirtualBox supports the display of a paravirtualization interface. One of the interfaces it provides is KVM. This KVM paravirtualization interface can be recognized by Linux kernels 2.6.25 and later. The Oracle VM VirtualBox implementation now supports paravirtualized clocks and SMP spinlocks.

What’s the Difference between Full Virtualization vs Paravirtualization?

The main difference is that paravirtualization requires the modified guest OS while full virtualization doesn’t. The modifications enable the guest OS to communicate directly with the hypervisor, which delivers better performance than full virtualization, especially in the early days of virtualization when full virtualization wasn’t supported by hardware-assisted virtualization.

Full virtualization isolates the individual VMs and simulates all the hardware resources, using binary translations to carry out operations. Meanwhile, paravirtualization enables the guest OSes to communicate directly with the hypervisor through hypercalls.

Full virtualization enhances isolation and security better than paravirtualization. In full virtualization, the VM is fully isolated from the host system because the hypervisor creates a fully virtualized hardware environment. This means the VM runs independently, reducing the risk of an attacked guest OS influencing the host system or other VMs. In paravirtualization, the guest OS is modified to communicate directly and efficiently with the hypervisor. The modifications might create attack surfaces. Also, any changes or updates could lead to compatibility issues.

Table: Difference between Full Virtualization vs Paravirtualization.

We also offer affordable bare metal servers from our site ServerDime. When needed, view dedicated servers and order your desired server. For VPS Servers, you can view virtual machine pricing and easily buy a VM (Virtual Machine) which is provisioned instantly.

Conclusion

In conclusion, virtualization is a transformative technology that maximizes IT resource utilization by enabling multiple virtual machines (VMs) to operate on a single physical server. Among the key approaches, full virtualization and paravirtualization offer distinct benefits and challenges tailored to specific use cases. Full virtualization simulates an entire hardware environment, allowing unmodified operating systems to run in isolated virtual environments. This method enhances security and simplifies system portability but may face performance overhead due to the complete hardware emulation required. Hardware-assisted virtualization has mitigated many of these limitations, making full virtualization a robust option for many organizations.

Paravirtualization, on the other hand, requires modifications to the guest operating system to optimize its interaction with the hypervisor. By eliminating the need for full hardware emulation, it offers improved performance and resource efficiency. However, this approach is limited by its reliance on compatible, modifiable operating systems, which can introduce compatibility challenges and potential vulnerabilities. The direct communication between the guest OS and the hypervisor, while efficient, reduces the level of isolation compared to full virtualization.

Ultimately, the choice between full virtualization and paravirtualization depends on the specific needs of the IT environment. Organizations must weigh factors such as performance requirements, system compatibility, security needs, and resource availability to select the most appropriate solution. Both methods remain valuable tools in modern IT infrastructure, enabling flexibility, scalability, and efficiency in managing computing resources.