OpenVZ is an operating system-level virtualization technology based on the Linux kernel and operating system. OpenVZ allows a physical server to run multiple isolated operating system instances, known as containers, Virtual Private Servers (VPSs), or Virtual Environments (VEs). It's similar to FreeBSD Jails and Solaris Zones.
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OpenVZ is an operating system-level virtualization technology based on the Linux kernel and operating system. OpenVZ allows a physical server to run multiple isolated operating system instances, known as containers, Virtual Private Servers (VPSs), or Virtual Environments (VEs). It's similar to FreeBSD Jails and Solaris Zones.
As compared to virtual machines such as VMware and paravirtualization technologies like Xen, OpenVZ is limited in that it requires both the host and guest OS to be Linux (although Linux distributions can be different in different containers). However, OpenVZ claims a performance advantage; according to its website, there is only a 1–3% performance penalty for OpenVZ as compared to using a standalone server. One independent performance evaluationHPL-2007-59 technical report, http://www.hpl.hp.com/techreports/2007/HPL-2007-59R1.html?jumpid=reg_R1002_USEN confirms this. Another shows more significant performance penalties(Ottawa) Linux Symposium Proceedings, Volume I, July 2008, http://www.linuxsymposium.org/2008/ols-2008-Proceedings-V1.pdf depending on the metric used.
OpenVZ is a basis of Parallels Virtuozzo Containers, a proprietary software product provided by Parallels, Inc. OpenVZ is licensed under the GPL version 2. OpenVZ project is supported and sponsored by Parallels.
The OpenVZ is divided into a custom kernel and user-level tools.
Kernel
The OpenVZ kernel is a Linux kernel, modified to add support for OpenVZ containers. The modified kernel provides virtualization, isolation, resource management, and checkpointing.
Virtualization and isolation
Each container is a separate entity, and behaves largely as a physical server would. Each has its own:
- Files
- System libraries, applications, virtualized
/procand/sys, virtualized locks etc. - Users and groups
- Each container has its own root users, as well as other users and groups.
- Process tree
- A container only sees its own processes (starting from init). PIDs are virtualized, so that the init PID is 1 as it should be.
- Network
- Virtual network device, which allows a container to have its own IP addresses, as well as a set of netfilter (
iptables) and routing rules. - Devices
- If needed, any container can be granted access to real devices like network interfaces, serial ports, disk partitions, etc.
- IPC objects
- Shared memory, semaphores, messages.
Resource management
OpenVZ resource management consists of three components: two-level disk quota, fair CPU scheduler, and user beancounters. These resources can be changed during container runtime, eliminating the need to reboot.
