An Introduction to Virtualization

JamieX writes "kernelthread.com brings you a very cool and instructional article in An Introduction to Virtualization... The piece talks about the history of VM's, why they are becoming important again, implementation issues and most of all a look at a large number of virtualization solutions for all kinds of operating systems... many of them barely known... essentially more than you want to know about virtualization on a single page! Great read and reference."

Comments

vmWare's ESX server uses Linux Kernel?

[stonebeat.org]

I thought vmWare's ESX Server used a Linux Kernel. Or is it just the installer that is based on Linux.

Re:vmWare's ESX server uses Linux Kernel?

[stonebeat.org]

ok I think I answered my own question. Here is what vmware says:
"VMware's patented and patent-pending technology serves as the foundation for VMware ESX Server; it is not derived from Linux or FreeBSD." @ VMware ESX Server 2 FAQs

Linux is only used a bootloader, and for I/O to the console on the ESX Server.

Re:vmWare's ESX server uses Linux Kernel?

[grunthos]

I'm an ESX user. I obviously can't verify whether the ESX kernel was "based on" Linux or not, but it presents an extremely effective appearance of being a Linux kernel to software running in the "console OS", the controlling part of the system

The console OS in ESX 1.5 and 2.0 is based on RedHat 7. We regularly install generic RedHat 7.1 or 7.2 RPMs for various things, like SMBFS or PAM modules, and it works perfectly.

It seems to me like the underlying VM controller is all new, like they say. But the console OS is a barely-modified Linux kernel running as a specially-privileged VM in the VM controller.

Re:vmWare's ESX server uses Linux Kernel?

[ninejaguar]

I got confused between ESX and GSX:

How Is ESX Server Different from GSX Server?
ESX Server is designed for up to 16 processor departmental and enterprise servers, and runs its virtualization layer natively on hardware. VMware GSX Server is designed for up to four processor workgroup and departmental servers. It runs as an application on top of a host operating system.

So, GSX runs as an app on Linux, while ESX runs linux as a service or maybe even as a library?

= 9J =

Re:vmWare's ESX server uses Linux Kernel?

[Anonymous Coward]

The Console OS (now "Service Console") in ESX is just a modified Linux kernel (the source is available under the GPL).

It is used as a bootloader, until the VMKernel is loaded and kicks Linux out from under it and begins running linux in a VM. Primarily Linux is used to run Apache for the MUI, VM management tools like serverd and hardware vendor specific management tools.

Lack of comments.

[lynx_user_abroad]

I take it from the lack of comments that most of the slashdot crowd is unfamiliar with this stuff.

There are certain advantages to having cut ones teeth on the IBM mainframe.

Heads-up, people. This stuff is way cool. Think of it like a MATRIX you own.

Re:Lack of comments.

[Slashamatic]

ABout the limit for many people here is vmware to run Windows under Linux (or vice versa), and UML because it is used by many hosting providers.

The problem comes down to the sucky IA-32 architecture which is hard to virtualize. Take a privileged mode instruction on a proper architecture, and it will trap allowing it to be emulated. Some IA-32 instructions do not trap but return different mode-dependent results. A nightmare.

For me what is interesting are domains, giving a very fine level of VMs to CPU allocation. A CPU may be reserved for a single VM or be shared by many, in turn many CPUs can be devoted to a single VM This gives very fine resource control and is what you get now on heavy iron such as the IBM Z-series or the big Sun machines.

This is why I follow the Xen project with some interest. Xen needs mods to the host OS to get around the shortcomings of the IA-32, but they are minor and well defined (replacement of some macros). It isn't there now, but maybe if they get enough people working on it, it could be very interesting indeed.

AMD64 support for virtualization?

[TheLink]

Whilst IA-32 is not virtualization-friendly, is AMD64 friendlier or will future versions be?

A few 0.5GB or 1GB VMs here and there and 4GB starts to look rather small. So if AMD64 has good VM support it just adds value.

Re:AMD64 support for virtualization?

[Anonymous Coward]

Unfortunately no. The popf debacle (among others) was not fixed in x86-64.

VMWare Vs. VirtualPC

[IDidn'tPostThis]

Does any body have opinions on whether VMWare or VirtualPC is better ? I'm looking at using some sort of VM to do Windows development under the various flavors of Windows

Re:VMWare Vs. VirtualPC

[Anonymous Coward]

If you just want to virutalize Windows, both will work fine. VPC seems better at old stuff like DOS games and OS/2, while VMWare focuses more on server partitioning.

Also, VPC is now included in the MSDN subscription, if that makes a difference.

Re:VMWare Vs. VirtualPC

[madhippy]

vmware probably a better all rounder - Virtual PC seems okay for one instance of a virtual pc - vmware seems to handle memory allocation of guests better .. .

Re:VMWare Vs. VirtualPC

[Anonymous Coward]

I have used both a lot and I'd say that Vmware offers better performance but that Virtual PC is more stable and easier to setup. In both the TCP/IP "virtual switch" can be troublesome, use the NAT mode networking if you can. All IMHO of course.

The article omits XEN & coLinux

[vinsci]

Oddly enough the article doesn't even mention XEN, one of the most interesting virtualization systems. Xen is being actively developed and has also been featured on Slashdot a couple of months back when they released the first public versions.

Also omitted is the new coLinux, which was discussed on Slashdot, too, just the other week.

Re:The article omits XEN & coLinux

[Abcd1234]

Oddly enough the article doesn't even mention XEN [cam.ac.uk], one of the most interesting virtualization systems.

Hardly... it's basically a standard virtualization architecture, where they've decided not to implement the hard stuff, meaning an OS needs to be modified to run on it. Sure, this makes it fast, but also relatively useless for most people.

As for colinux, it's really just another type of User Mode Linux, where the underlying OS is Windows, rather than Linux. The point being that it's not a virtual machine in the traditional sense.

Far more interesting and useful, IMHO, was the (now defunct) Plex86 project, or for x-platform emulation, the (active) QEMU project.

Two Different Beasts

[TheRealMindChild]

Virtual PC is a full blown x86 machine emulator. VMWare is MOSTLY a virtualizer... meaning it passes most calls directly to the hardware... which also means it will only work on x86 hardware.

Re:Two Different Beasts

[tepples]

You seem to confuse two different products. Virtual PC for Mac is a full-blown emulator, as you correctly state. However, Microsoft also sells Virtual PC for Windows, which is a virtualizer like vmware.

Xen and the art of virtualisation....

[Slashamatic]

There are two approaches to virtualisation, one where you mod the guest OS and thother where try to virtualise hardware instructions that were never designed for it (Thanks Intel). You can guess which is cleaner, faster and more reliable.

If you can compile Linux, you can run Xen. If you can compile Windpws XP, you run it under Xen too (not permissable for most of us, but they could and did). What is interesting is that are looking very much at the administrative side, possibly more so than vmware.

Wow! New technology from 1967

[Dark$ide]

IBM have been doing this on s/360 since CP/67.
It's hardly new and I can't see how VMWare can get a patent, it's prior art.

Don't forget about vservers

[UNIX_Meister]

Don't forget about Linux Vservers. They allow you to have multiple virtual machines running on a single physical machine, all separated for security reasons. So you could run ftp on one, and a web server on another, and they would be as separate as physical machines. Also, I use VMware daily to run office-type applications, Outlook, and Remedy. I'm forced to by my employer, and the VMware solution let's me keep my regular linux wrapper around windows. Also, since the vpn connection takes control of the box, I still have "real" network access with my linux box.

No inferno?

[Anonymous Coward]

You write an article about virtual machines but don't mention Inferno? It's one of the best examples of a virtual machine!

Here's a link for Inferno

[DrSkwid]

http://www.vitanuova.com/inferno/

Inferno was started by Bell-Labs and then sold on to Vita Nuova for commercial exploitation.

It has always been a free binary downlaod with source for userland and kernel source for pyament, but now, in the 4th edition, the whole kit and caboodle is under a dual license.