OpenVZ is a virtualization technology based on the Linux kernel and operating system. OpenVZ allows a host server to run multiple isolated operating systems, known as virtual servers or containers.
OpenVZ is limited in that it can only run Linux operating systems, compared with virtualisation software such as VMware and paravirtualization technologies like Xen which can run many different types of operating system. However, OpenVZ has a performance advantage; according to its website, there is only a 1–3% performance penalty for OpenVZ as compared to using a standalone server.
OpenVZ virtual machines are jailed containers and not true virtual machines like those using VMWare and Xen. OpenVZ uses a single Linux kernel that is patched to enable OpenVZ to work and therefore it can only run Linux, however it is this same disadvantage that becomes its advantage because it doesn't have the overhead of a true hypervisor like VMWare. Memory allocation is soft in that memory not used in one virtual environment can be used by others.
OpenVZ uses a common file system so each virtual environment is just a directory of files that is isolated using chroot. This is of great benefit when it comes to backing up a container as all that is required is a copy of the directory containing the virtual server files. This can easily be synchronised using software like rsync to take incrmental backups.