Virtualization has become the choice of many organizations to build a more “now” IT infrastructure with higher flexibility and computing performance. It makes a single server able to mount multiple operating systems for optimal resource utilization, and the core component behind this technique is called the hypervisor.
Updated by Nick Zhao on 2022/09/08
Virtualization has become the choice of many organizations to build a more “now” IT infrastructure with higher flexibility and computing performance. It makes a single server able to mount multiple operating systems for optimal resource utilization, and the core component behind this technique is called the hypervisor.
QEMU and KVM are two hypervisors that virtualize physical server in different ways. Before we dig deep into this topic, it’s necessary to know some basic knowledge about the types of hypervisors. All available hypervisors on the market can be divided into two types: type-1 hypervisor and type-2 hypervisor.
Type-1 hypervisor is also called bare-metal hypervisor, which directly runs on hardware without host OS needed. KVM is a type-1 hypervisor.
Not like type-1 hypervisor that can directly interact with the hardware resources, type-2 hypervisor needs host OS to be the intermediary between itself and hardware, which means it runs on an installed host OS. QEMU can be seen as a type-2 hypervisor.
QEMU is an open-source machine emulator, it can be directly installed on the operating system. QEMU emulates CPU and other hardware resources for Guest OS through dynamic binary translator technology, which makes the Guest OS thinks that it directly interacts with hardware. QEMU will then translate these interactive commands to the hardware to make it implement the corresponding operations. However, since all commands from the Guest OS have to go through QEMU emulation, there’s a lack of high performance when compared with KVM.
KVM (Kernel-based Virtual Machine) is a fork of QEMU. It is an open-source hypervisor that runs on hosted Linux OS. It means that to use KVM you need to install a Linux OS as the host OS first. The reason why it’s still a type-1 hypervisor is that it works to convert the host OS into hypervisor with loaded kernel modules like kvm.ko, kvm-intel.ko, and kvm-intel.ko.
Typically, QEMU is used along with KVM. On the one hand, QEMU does not have the capability for hardware acceleration, which will make virtual machines have very poor performance, and KVM can help on that. On the other hand, KVM cannot virtualize some specified hardware device like network cards and disks, and QEMU can help on hardware virtualization. Therefore, we can say that QEMU and KVM are complementary components that makes a perfect virtualization solution.
KVM has been applied into many vendors’ enterprise-grade virtualization solutions, for example, Oracle Linux Virtualization Manager, oVirt/Red Hat Virtualization, and Huawei FusionCompute (KVM). This in some way indicates its high reliability and availability without saying.
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