How is XEN different from OpenVZ?

Question

OpenVZ

I know only two differences - the ability to put different operating systems in containers and the ability to give devices to a specific container. Well, and “a more honest distribution of processor time” - what is “more honest” is not clear, but let it be more.

Are there any more "obvious" advantages?

Answer 1

Here are the popular systems in descending order of functionality:

Xen - an order of magnitude more complicated and functional, in addition to the paravirtualization mode (like openvz), it has a full virtualization mode (including support for the corresponding features of processors), there are mechanisms for transferring iron inside the virtual machine (for example, support for not the weakest intel video cards), snapshots, migration, ... many many tasty features.
VMWare - like xen, it is complex, fancy, seasoned with the appropriate infrastructure and good outrageous prices :)
kvm / qemu does not have a full-fledged paravirtualization mode- full processor emulation (as well as virtualization through processor support), there are goodies from 'big brothers' like migrating a running virtual machine over the network, transferring hardware (much worse support than xen / vmware), etc. can be considered a backend, since it does not have a GUI in ideology, it is sawed by those who wish
VirtualBox - processor emulation, incl. use of processor virtualization support, ideal as a standalone desktop application, no network migration, there are snapshots, some goodies are hidden from the GUI in the
OpenVZ command line- this is the operation of all machines on one core (patches for it are called openvz), there is no virtualization, maximum speed (since it is actually an extended chroot with isolation). To launch the kernel module, you need to go to the host system and its administrator (for example, tun / tap adapter for firstvds is given on request)
There are no snapshots (but they are implemented through lvm), there is a migration, there is a dump of the container state to disk and the resumption of work ...
Lxc - even easier than openVZ, there is not even proper isolation (if you fuss, you can, having root in the container, go to the host system with root access), a direct analogue of jail in freebsd, it makes sense for tricky network configurations, tests, etc.
chroot- this is not even a virtual machine, it's just the simplest isolation within the file system, substitution of paths in calls to file functions.
ps lxc also called 'chroot on steroids'

OpenVZ / lxc / chroot support almost full cascading of virtual machines (i.e. for example, you can run kvm / virtualbox inside the openvz container if there are modules, even with support for hardware acceleration)

Answer 2

Yes, they are two completely different systems.
One openz - pseudo

Answer 3

By the way, another very important note:
* xen/vmware/virtualbox/kvm - can only work with containers, ie. the host system does not mount the disks of guest containers (but it can do this through snapshots, for example) - this means the hoster has limited access to the data of its clients. Since it is quite possible for these technologies to create their own virtual machine, with their own kernel and initramfs loader, true paranoids create an encrypted container, and enter the password via ssh into the initramfs. To access the data of such a machine, you will need a little more than just administrator rights (in a simple case, you will need to study memory dumps, and in a complex one, you will need specialized hardware and a lot of money)
* openvz/lxc/chroot - the virtual machine's file system must be mounted on the host system, file encryption, etc. actually inaccessible (protecting data from the hoster is unrealistically difficult, but you can play around with cascading virtual machines)
Hoster access to data is a very important point for some projects (hello the linode provider and a lot of bitcoins stolen, which theoretically served as the main cause of the death of the bitcoinica service).

Answer 4

there is no swap in
openvz openvz "dishonestly" considers memory consumption (by VSZ and not by RSS)
in openvz there is no ppp, encryption of block devices
in openvz container admin can enter "just like that", without password and password reset procedure with rebooting the server
in openvz a lot other limitations besides memory, which are often skewed and interfere with normal operation

Answer 5

Comparing Virtual Machines
It's not easy to compare Xen and OpenVZ and choose one. It all depends on the specific task.
PS: there is also KVM