Understanding the differences between KVM and Hyper-V is essential when building a virtualized environment to optimize hardware resource utilization for an organization. In this blog article, we briefly explain what KVM and Hyper-V are, and then compare the two hypervisors.
The key points of this comparative evaluation are as follows:
- Scalability and performance
- Management tools
- Memory provisioning options
- Security features
- Live migration capabilities
What is KVM Hypervisor?
The KVM acronym stands for Kernel-based Virtual Machine. It is an open-source full virtualization solution in the Linux kernel. KVM runs on x86 processors, providing users with hypervisor capabilities to build virtualized environments.
The Kernel-based Virtual Machine hypervisor was first released in 2007 as part of Linux versions 2.6.20 and newer. KVM supports various OSs such as Linux, Windows, macOS, and Haiku, offering hardware-assisted virtualization capabilities. The same solution also provides paravirtualization for Windows, OpenBSD, FreeBSD, among other systems.
KVM can be used on the majority of Linux machines that have CPUs supporting hardware-assisted virtualization. To install KVM, you need to download the required packages from Linux software repositories, plus kvm-qemu and a management tool (optional).
The most common KVM-based virtualization management tools are Oracle Linux Virtualization Manager, Proxmox VE and Red Hat Virtualization Manager.
What is Hyper-V?
Hyper-V is a native Microsoft hypervisor that enables the creation and use of VMs and virtual environments. Hyper-V can be run on an x86-64 system under Windows OS.
Microsoft Hyper-V was first released as part of Windows Server 2008. The hypervisor is an optional downloadable component of Windows Server systems. In addition, Hyper-V has a standalone free edition with limited functions and that only supports CLI (command-line interface).
With Hyper-V, you can get a set of virtual machines isolated from each other. This is possible because of the specific parent (root) and child partitioning. A parent partition, which can directly access hardware, runs the virtualization management stack. Then, this partition creates child partitions that host guest operating systems.
KVM vs Hyper-V: A Detailed Comparison
Now that we highlighted the general differences in our Hyper-V vs KVM comparison, we can proceed with more details. Check the information below so you can choose the solution that best fits your needs.
Scalability and performance
Scalability and performance are arguably the two most important points in any KVM vs Hyper-V comparison. The good news is that the competition here results in a draw – both Hyper-V and KVM have high performance and provide great scalability.
The KVM virtualization software is based on the Linux kernel, which is an open-source solution. This means that KVM can run properly on a wide range of hardware. The same Linux kernel enables high efficiency and operational speed.
On the downside, the open-source nature of KVM can lead to situational issues that can take time and effort to troubleshoot. Still, KVM’s online knowledge base is substantial, meaning that you can most probably find your solution quickly.
On the other hand, Hyper-V is Microsoft’s proprietary hypervisor packed together with the Windows Server OS, optimized to provide maximum performance on the majority of available hardware. Hyper-V scalability also allows you to use your IT infrastructure at top efficiency by running multiple VMs on the host and scaling your virtual workloads up and out on demand.
The main disadvantage of Hyper-V is its limited support for operating systems other than Windows. Combined with certain management complexities and potential compatibility issues, Hyper-V can also be challenging if you don’t have the required tech experience.
Management tools
As Hyper-V and KVM are designed for different underlying platforms, their management tools differ as well.
For Hyper-V management, you can use the Windows PowerShell CLI. In case you want a solution with a GUI, you might want to use Windows Admin Center or Hyper-V Manager.
Additionally, organizations can reap multiple benefits from the native enterprise-grade management tool provided by Microsoft: System Center Virtual Machine Manager (VMM) for Hyper-V. Admins usually prefer VMM to manage Hyper-V environments due to the convenient and informative infrastructure view and scalability capabilities. On the downside, you need to purchase a dedicated license to use Virtual Machine Manager.
You can perform all KVM management tasks using only the CLI, just like with Hyper-V via PowerShell. Still, those preferring graphic interfaces to manage their KVM infrastructures might want to try solutions like Morpheus, virt-manager, or Cloonix, among others.
Hyper-V and KVM share one significant feature: a vast hardware compatibility list, which provides great flexibility.
For KVM, you can effectively use any storage (including direct-attached and network-attached storage). In turn, Hyper-V works with any storage with Windows support. Keep in mind that if you plan on storing VM files on a NAS or network file share, you’ll need to configure server message block protocol 3.0.
Memory provisioning options
Memory usage flexibility is another advantage shared by KVM and Hyper-V. Both hypervisors can use regular memory or NUMA (non-uniform memory access) equally well.
However, it is worth noting the difference between KVM and Hyper-V in dynamic memory allocation. In Hyper-V, the dynamic memory feature enables virtual machines to regulate memory usage depending on the current VM needs. The demand does not exceed the set memory volume limits. With dynamic memory allocation, administrators can run more VMs on a single host by overprovisioning memory.
The KVM hypervisor also enables memory over-provisioning. However, the feature implementation is a bit different from that in Hyper-V. KVM virtual machines are separate processes running on the host under Linux OS. Thus, the VMs don’t have pre-allocated memory volumes. The operating system distributes memory between virtual machines based on requests. In simple words, the KVM virtualization software allocates memory blocks to each virtual machine on demand.
In case a KVM host faces physical memory deficiency, the system then sends some memory pages to swap. The amount of free RAM then increases on demand, thus enabling memory overcommitment for the host system.
Security features
When it comes to the security capabilities in the KVM vs Hyper-V comparison, both solutions have efficient security features that you can use to ensure the protection of your organization’s data and environment.
For KVM, VM isolation and security come from the capabilities of two solutions. The first one, SELinux (security-enhanced Linux) sets a security perimeter around virtual machines. sVirt (secure virtualization) enables MAC (Mandatory Access Control) security for guest VMs, adding more capabilities to SELinux and reducing the impact of human errors on virtual security.
Hyper-V can also isolate virtual machines to secure the environment before a single compromised node. Additionally, the Secure Boot feature available with gen 2 Hyper-V VMs helps prevent unauthorized OS, drivers, and firmware from running at boot time. Additional security capabilities of Hyper-V include traffic encryption on an entire subnet, Guarded Fabric (an anti-malware security model), and shielded VMs.
Live VM migration capabilities
Live migration of virtual machines is a feature available in both KVM and Hyper-V. With this feature, administrators can move VMs to a different server without interrupting VM operations.
Live migration can help organizations support production continuity and service availability. For instance, when you have a planned hardware maintenance session on your main virtualization host, you can move your crucial VMs to a secondary server. The maintenance then runs as intended without disrupting your organization’s workflows and operations.
Additionally, sometimes your host has insufficient resources to run the VMs you originally created on it. For example, a VM can become too “large” during use and cause performance issues for the entire host. The most effective way to optimize host performance is to use your hypervisor’s live migration capabilities to move that virtual machine to a different host without turning off the VM.
Conversion Between KVM and Hyper-V
When necessary, you can convert KVM virtual machines to work in Hyper-V environments and vice versa. Check the guides on conversion between KVM and Hyper-V below.
Converting from KVM to Hyper-V
Converting KVM virtual machines to use in Hyper-V environments is done in three steps:
- Install qemu-ing.
- To convert a KVM virtual machine disk image to the Hyper-V format, use the following command:
qemu-img.exe convert sourcefile.qcow2 -O vhdx -o subformat=dynamic destinationfile.vhdxIn this command, sourcefile is the source VM disk file name and destinationfile is the new disk file name you want to get after conversion.
- Create a new virtual machine in Hyper-V, then attach the converted disk image to it.
Converting from Hyper-V to KVM
To convert Hyper-V VMs to KVM environments, do the following:
- Turn off the Hyper-V VM that you need to convert. Then choose the VM, and, in Hyper-V Manager, hit Export.
- Provide the destination repository for the VM files.
- Note the exported VM’s processor cores, memory, and MAC.
- Copy the VHDX file of the target virtual machine to the KVM environment.
- On the KVM host, install virt-v2v.
- Use virt-v2v to convert VHDX to QCOW2 with the following command:
sudo virt-v2v -i disk sourcefile.vhdx -o local -of qcow2 -os targetfile - After the conversion is over, note the guest OS.
- Use VMM to create a new virtual machine in the KVM environment.
- Choose Import existing disk image, then click Forward.
- Find the vhdx-sda file, then specify the OS you need to install. After that, hit Forward.
- Complete the initial new VM configuration: set memory, CPU, VM name and specify KVM networking settings. Then, click Apply.
- Configure specific options such as MAC here. Then, at the top of the window, select Begin Installation.
Cost Considerations
The organization’s budget remains the cornerstone of any choice regarding IT environments, and the decision about KVM vs Hyper-V is no exception. When it comes to pricing, KVM has a clear advantage: as an open-source solution, it is free to use. Plus, you can also download and install the management tools and feature modules at no additional cost. Microsoft Hyper-V module is also available for free. However, the nuance is that Microsoft recommends upgrading to Windows Server to run Hyper-V virtualized environments.
Conclusion
The final choice between KVM vs Hyper-V depends on your organization’s specific needs and budget. In case you need to run Windows VMs in a familiar ecosystem and you are ready to allocate funds to get the proprietary supported solution, Hyper-V is the right option. On the other hand, if you are ready to put additional effort into configuring and adjusting the open-source solution, KVM can provide nearly equal capabilities and experience in terms of management, security, scalability and features, all for free.