What is KVM?

How Does KVM Work?

It works by leveraging the extensions built into modern CPUs (like Intel VT-x or AMD-V). These extensions allow the processor to support multiple OS running simultaneously in isolation.

When installed on a Linux host, it turns that host's kernel into a hypervisor. This can then create and manage VMs, and the process looks roughly like this:

• CPU virtualisation extensions: The CPU's virtualisation extensions enable the machine to distinguish between the host OS and the guest OS running in VMs.
   
• Linux kernel as hypervisor: KVM utilises these extensions to create a virtualised environment directly within the Linux kernel. The kernel itself acts as the hypervisor, managing the VMs and allocating resources like CPU, memory, and storage.
   
• Guest operating systems: Each VM runs its own guest OS, which is isolated from the host and each other, providing a secure and stable environment.
   
• Virtual devices: It configures virtual devices to the guest OS, such as virtual network cards, hard drives, and USB controllers. In turn, virtual devices allow these OSs to interact with the underlying hardware.
   
• QEMU for emulation: While it enables the core infrastructure, it often works in conjunction with QEMU (Quick Emulator). QEMU emulates the hardware for the virtual machines, allowing KVM to support a wide range of options. QEMU also provides a user-space interface for managing it.

The software's net effect is that it takes advantage of a CPU's hardware server virtualisation capabilities and the Linux kernel's flexibility to create a highly efficient and integrated platform.

KVM offers a compelling set of features, starting with its native integration within the Linux kernel. Native integration provides access to the stability, performance, and robust security of the Linux OS.

Furthermore, it takes advantage of hardware-accelerated virtualisation, leveraging processor extensions (Intel VT-x or AMD-V) to achieve near-native performance, minimising overhead and maximising efficiency.

It enables a diverse range of OS to co-exist, including various Linux distributions, Windows, and more. Live migration is a key capability, enabling these to be moved between physical hosts without any downtime, which is crucial for maintenance, resource balancing, and ensuring high availability.

There’s also flexibility in storage options, supporting everything from local disks to network storage such as NFS and iSCSI, as well as shared storage. That includes support for network-attached storage (NAS). Advanced memory features, such as dynamic memory allocation and memory ballooning, further contribute to efficient resource utilisation.

Scalability and Flexibility for IT Environments

It excels in providing scalability and flexibility for IT environments. Whether you're running a small business or managing a large data centre, KVM can adapt to your needs. It allows you to easily scale your virtualised infrastructure up or down as demand changes.

New VMs can be quickly provisioned, and existing ones can be resized or migrated with minimal disruption. This flexibility extends to the choice of hardware and software, as it is compatible with a wide range of systems and supports various operating systems. This adaptability makes KVM an ideal solution for dynamic IT scenarios where resource needs fluctuate.

Cost-Effective Virtualization Solution

KVM presents a highly cost-effective virtualisation solution. Because it is integrated directly into the kernel, there are no separate licensing fees for the hypervisor itself. This significantly reduces the total cost of ownership compared to proprietary solution platforms.

It also boosts public cloud security and private cloud security. In public cloud deployments, KVM's isolation capabilities help protect tenant workloads from each other, a critical component of maintaining public security. Within the private cloud, KVM offers similar benefits, enabling organisations to create secure, isolated environments for sensitive data and applications.

Furthermore, the open-source nature of this software allows you to avoid vendor lock-in and gives you greater control over your virtualisation environment. You can choose the support and maintenance options that best suit your needs and budget. This cost-effectiveness makes KVM particularly attractive for businesses looking to optimise their IT spending.

Open-Source Benefits for Enterprises

The open-source nature of KVM benefits enterprises because it fosters a vibrant community of developers and users, leading to continuous improvement, rapid bug fixes, and a wealth of available resources.

This community-driven development ensures that the software stays current with the latest technologies and best practices for security. Enterprises also benefit from the transparency and flexibility of open-source software. Companies can inspect the code, customise it to their specific requirements, and contribute back to the community. This level of control and collaboration makes KVM a powerful and adaptable solution for enterprises.

Role of the Hypervisor in KVM

In KVM, the Linux kernel itself acts as the hypervisor. This is a key distinction from some other options that utilise a separate, dedicated OS. The hypervisor is the software layer that creates and manages virtual machines. In KVM, the kernel leverages CPU extensions (Intel VT-x or AMD-V) to create a virtualised environment.

The kernel allocates resources, such as CPU, memory, and storage, to the guest operating systems running within the virtual machines. Because it is integrated directly into the kernel, KVM benefits from the speed, stability, and security features of the OS. This tight integration also minimises overhead, resulting in near-native performance for the machines.

KVM vs Other Virtualization Solutions

KVM's architecture differs significantly from other solutions. Some platforms, such as VMware ESXi, use a type 1 hypervisor (also known as a bare-metal hypervisor). A Type 1 runs directly on the machine without an underlying OS.

In contrast, KVM is a type 2 (or hosted), as it runs on top of an existing operating system. While type 1 hypervisors can offer slightly better outcomes in some cases, its close integration with Linux provides its own speed advantages and greater flexibility.

Compared to other type 2’s, such as VirtualBox or VMware Workstation, KVM's integration with the kernel and its use of CPU extensions provide significantly better speeds and scalability.