However, some litte comments… You said “all virtual machines must run the same operating system [using paravirtualization]“. I should say this is not necessarily true, at least for Xen. Each domU (the term to refer to virtual machines in Xen parlance) can use a different kernel version (you set it with the ‘kernel’ parameter in the domU configuration file). Beyond the kernel, each domU can use a different filesystem (i.e., virtual disk), set with the ‘disk’ parameter.

In addition, I should add another kind of virtualization to the list, usually knows as system-level or operating system virtualization. Some examples are Linux Vservers, FreeBSD jails and OpenVZ/Virtuozzo (the one you mentioned! :). Some people consider they aren’t a true forms virtualization, but the true it’s that they provide isolated execution environment in a lighter way than the other approaches (hardware virtualization, either application or hypervisor based, and paravirtualization). And, in this case, all these environments share the same operating system.

What they do all share is a reliance on the host _kernel_ for scheduling and maintaining isolated processes.

Virtualization 101 got me closer, but didn’t tell me where to start.
bruce

Clearly one option (Which I know has its down side) is to combine the functions of a number of servers onto one but how much throughput can be expected from a virtualised machine compared with a native machine?

Roland Pullen

The operating system is more than the kernel, so my statement should be “all these environments share the same _kernel_”, as you said. Operating systems (each one contained in a isolated root filesystem in the hosting machine) can vary.

I know a bit about FreeBSD and Linux Vservers and they behave the same way (i.e., same kernel, different per-filesystem operating systems).

Specially when paravirtualized OS or the hardware extensions provided by the main CPU vendors (Intel VT-x and AMD-v) are used.

Your las paragraph also bring an interesting point. Virtualization doesn’t necessarily means to split a physical machine into multiple virtual machines, but also to aggregate the combined power of several physical machines into one big virtual machine. What virtualization actually means the decoupling logical resources from physical infrastructure, no matter if this decoupling is N:1, N:1 or even 1:1. Have a look to PVM, for example.

[...] What virtualization actually means is the decoupling of logical resources from physical infrastructure, no matter if this decoupling is N:1, 1:N or even 1:1

:)

Although its name (Parallel Virtual Machine), PVM has nothing to do with virtualization. It is a library for message passing programming, and, by the way, a library that is in decline.

So yes, virtualization actually means the decoupling of logical resources from physical infrastructure, but I don’t think that PVM is a good example for that.

… Virtualbox host can be Lin/Win/Mac, guests can be Win/Lin (probably Mac too)
as demonstrated more clearly in screenshots
http://liquidat.files.wordpress.com/2007/09/virtualbox150_nahtlos_linuxhost-winxpguest21.jpg
http://www.virtualbox.org/attachment/wiki/Screenshots/VirtualBox_OSX_beta_3.png

Disclaimer: I do not work for, nor am I affiliated with Innotek or Sun Microsystems.

In VMWare server version 1 and 2 Host interface bridging just works by choosing the bridging option. That’s it! But where I can barely run one vmware vm on my host with AMD64 X2 and 2 GIGs of RAM, I can run 3 or 4 VirtualBox vm’s at once on the same system.

The web interface brings networking to a screeching halt because of bandwidth in VMWare.

So it all depends on what’s important to you as to which one to use but either one will work with Linux or Windows as a host and Win/Linux guests. Even virtual windows servers and linux servers. Virtualization is awsome!!

This is the right time when we are in stream where we are getting freedom to use and spread virtualization, so we all have to jump in it and have to enjoy it.

Why should not?

Regards,
Ashish Barot.