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OS Virtualization Interview
VirtualizationBuff writes "KernelTrap has a fascinating interview with Andrey Savochkin, the lead developer of the OpenVZ server virtualization project. In the interview Savochkin goes into great detail about how virtualization works, and why OpenVZ outshines the competition, comparing it to VServer, Xen and User Mode Linux. Regarding virtualization, Savochkin describes it as the next big step, 'comparable with the step between single-user and multi-user systems.' Savochkin is now focused on getting OpenVZ merged into the mainline Linux kernel."
Uhh... these products aren't aimed at your desktop box. They're for use in server farms, where virtualization provides an additional measure of security, along with providing the server operator more flexibility in how their hardware is utilized.
"why OpenVZ outshines the competition, comparing it to VServer, Xen and User Mode Linux."
/. submitter, but Andrey slants it a little too.
Of course, Andrey works for the software company that wrote this thing, and their closed full-featured flavor, Virtuozzo. The VZ method is a good one, and has excellent performance, but it has its drawbacks, too. Personally, I don't like that my VPSes need to use my VPS provider's kernel, which lacks features I desperately want (like stateful iptables matching), and which forces me to reboot whenever they upgrade their kernel (my VPS can't be migrated to a host running a different kernel), and I can't upgrade until my provider does.
VServer, Xen, and UML all make different tradeoffs. VZ goes for performance. Saying one outshines the others is just trolling. That's mostly on the part of the
I don't want to crap on the OpenVZ project. They're working on very cool stuff, and I applaud SWSoft for opening the thing up. I just want people to keep the comparisons in context.
In the mid 60's IBM created CP-67 which virtualized the IBM S/360. In the following years the system became VM/370, and has evolved to z/VM today http://www.vm.ibm.com/. VM (the general term for z/VM) is made up of two primary components, VM/CP (control program) and VM/CMS (a mini single user operating system). VM/CMS provided the ground work for being able to administer the system, and provided a nice programming environment in that each VM/CMS user had their own "system" that one could edit, compile and run their programs in an interactive environment (think of a MS-DOS type of model -- then remember that this was in the late 60's).
p / was written as a CMS application. As well as several native VM webservers.
CMS itself provided some limited simulation of IBM's two other mainframe operating systems OS/360 and DOS. Enough that one could write simple OS or DOS programs and do at least some unit testing. The simulation by CMS was by providing a limited set of the OS and DOS API.
Unlike MVS or DOS, (or even the CP/M, Windows, or *nix families) VM/CP itself does not provide many services directly. VM/CP does not provide any filesystems, any application APIs, etc. All VM/CP really did was to provide a barebone virtual machine and only provide those services one would find on the bare hardware. It was the responsibilty of the operating system running within the virtual machine to provide the application API, filesystems, application memory management, etc. Communication between vm's were originally only via the raw hardware model (channel-to-channel adapters, shared disk volumes, and a method of "punching" virtual cards and sending the virtual cards to another vm's virtual card reader.) As time progressed, VM/CP did provide some API's that allowed very simple messaging between two vm's (first VMCF - Virtual Machine Communication Facility, and then IUCV - Inter User Communication Vehicle).
Early on it was "discovered" that the virtual machine model made a lot of sense as a method to implement VM services. For example if one were to look at a modern VM system, you would see that the entire native VM TCP/IP stack is managed within a small collection of vm's. (Under VM/CP, a vm is called a "userid"). The native VM TCP/IP stack consists of a TCPIP userid that manages the network interface devices, and the TELNET server. The FTP userid implements the FTP protocol, etc. Each userid is totally seperate from the rest of the system and from each other (the tcp/ip socket facility "rides" on top of IUCV in a transparent fashion so that a tcp/ip server is coded the same as on *nix).
Because of the facilities provided by CMS, it is fairly easy to write little servers. For example the orginal LISTSERV server http://www.lsoft.com/products/listserv-history.as
If one wants to see what is and has been possible in a virtual machine environment, one should at least look at the history of IBM's VM.
For an excellent history of VM http://www.princeton.edu/~melinda/
and the VMSHARE archive, an early BBS used by VM system adminshttp://vm.marist.edu/~vmshare/