About virtualization technologies Xen, VMware ESXi, KVM, OpenVZ

Xen is a cross-platform hypervisor (a program or hardware system that allows multiple operating systems to run simultaneously on a single computer). Distributed under a free license, which does not require acquisition costs. Takes up little space when installed. Installed on most Linux operating systems (Debian, Ubuntu, RHEL, CentOS, OpenSUSE, etc.), as well as FreeBSD.

A key feature is support for paravirtualization mode. This technique allows the guest OS to perform almost like a real, non-virtualized system. The downside of this technique is the need to make changes to the guest OS kernel, which prevents it from being used on Windows systems where the kernel is closed.

Another nice feature of the Linux base system is the automation of processes using scripts. True, the standard package does not include a program with a graphical interface for management, which, at first glance, may seem like a minus, especially if you are just starting to get acquainted with this technology.

ESXi is a hypervisor from VMware, the main feature of which is installed directly on the hardware, which allows you to remove the "layer" between the physical resources of the machine and the hypervisor. Equipped with a convenient centralized graphical console, as well as management monitoring. This allows you to have full control of the VM for interaction functions such as rebooting, mounting ISOs, etc. It has a high-quality system of "on-the-fly migrations", which allows you to transfer the VM to another location with virtually no delay and deploy it there. Enterprise-level product for use in high-load projects. But due to the specifics of the OS, process automation is complicated. In addition, it has a paid license.

A small comparison table between Xen and ESXi.

OpenVZ is a time-tested technology that attracted many by the opportunity to sell services cheaper and provide those hardware resources for sale that did not exist. This is due to the device of the so-called counters, which, for example, do not act quite correctly when sharing memory. Another obvious disadvantage is one core for all, which means that it is impossible to make any changes to it inside the VM. In addition, if someone's file system "spoils", then this will affect all VMs on this machine. And it is also worth noting: that since this technology uses only a modified Linux kernel, it does not support any other OS for installation on a guest system.

KVM is a powerful virtualization technology that is already built into the Linux kernel (since version 2.6.20). Rich in functionality and features. Each VM has its own, full-fledged kernel. Works in conjunction with drivers from qemu, which is actively developed. Of the minuses, one can note the lack of paravirtualization that Xen has, and the need to install Linux or FreeBSD as a basis (when compared with ESXi). Also, there is no graphical management console by default.

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