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An Overview of Virtualization Technology
Jane Walker writes to tell us that TechTarget has a short writeup on virtualization and some of the ins and outs of using this technology effectively. From the article: "Virtualization is a hot topic in the enterprise space these days. It's being touted as the solution to every problem from server proliferation to CPU underutilization to application isolation. While the technology does indeed have many benefits, it's not without drawbacks."
From TFA:
.... [summary]'. That's a really broad and sweeping statement to make.
:) This is not a pro Xen rant but I'd like to point out that it does install effortlessly on most Debian systems in under an hour, the TFA sort of indicated otherwise.
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Novell is investing lots of effort in optimizing Xen specifically for running a virtualized copy of NetWare on top of Linux. The company's goal is to provide its customers with a migration path over to the Linux platform without giving up NetWare.
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One of the many un-sung uses for Xen is a swiss army SAN. I'm glad to see someone touch on this.
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If you want to use Linux as your host OS, you'll definitely have to go with VMware.
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That wasn't so cool. I appreciate the fact that there are just too many products available to touch on everything in one short summary article / writeup, and while the majority of the article was informative even to the lay person, you need to end a sentence like that with a 'Because
Or perhaps even "I recommend VMWare" would have been better.
It looks like the author lost interest in what they were writing near the end of the article. They talk about IRC or newsgroups being the only support options available for OS products [another sweeping statement], however have you checked out the wiki at xensource.com lately?
Just seems like TFA lost coherency after 'What's best?' It went from really informative to misleading rather quickly. If your going to go to a virtualized platform you owe it to yourself to spend a month trying each candidate to see what works best for you, not the author of whatever article you read
One thing the article does not speak about is licensing issues when using Virtulization. For instance MS has some twists and turns...
/ PUR.aspx
For instance:
One needs 2 different licenses if you run XP in XP.
You can run 4 instances of Windows Server for free in Windows Virtual Server.
You can run one copy of an older windows for free in Windows Vista.
(You can read more about this on the MS site...)
For Windows XP General Purpose license User Rights:
http://www.microsoftvolumelicensing.com/userights
Download and read document, section "Microsoft Desktop Operating Systems" which reads:
I) Installation and Use Rights.
a) You may install up to two copies of the software on one device.
b) Except as provided in Section II.a and II.b below, only one user may use the software at a time.
c) You may run a prior version in place of the licensed version for either or both of the copies.
d) You may only use the copies on the device on which you first install them.
e) You may use the software on up to two processors on that device at one time.
Thus this means that I can install and use XP as Bootcamp native and Parallels VM guest using only one license.
yay!
Seriously, how did this make it on /.? The article is only a few paragraphs long, doesn't really even touch on hardware virtualization support or why its necessary (because virtualization currently sucks under 'normal' intel architecture). It even refers to qemu as virtualization, which its not, its an emulator. It mentions the program once then never touches on it again. It never explains why a person might want to use bochs or qemu even though its much slower than vmware/virtual pc. it doesn't touch on parallels or any other software out there.
Even more it doesn't even explain why the suggestions it makes are made. This article is basically a badly written advertisement for vmware or virtual pc.
I have been using a few Xen based virtual servers from a commercial company recently - I used to manage physical machines. Here are some of my thoughts:
Advantages:
* Low performance overhead of Xen compared to other virtual solutions, and full OS level access as if it was a normal server.
* The cost of a hosted Xen solution is very low given that the hardware is usually managed.
* Reduced/No trips to the data center to replace hard disks etc,
* From the provider i use you can also reinstall the OS, snapshot and restore snapshots over a web interface and get access to the console. These are features you can set up in your own data center but most people never get round to.
* Quicker turn around if you need new servers, since normally they already have the spare hardware it's 1 or 2 days to get a new server set up rather than 1 to 2 weeks to order, install and configure it.
* You could do loadbalancing over several Xen Virtual hosts on physically separate machines very cost effectively. This would also mitigate against the variable performance on different Xen hosts if you used a dynamic weighting loadbalancer.
Disadvantages:
* Sometimes other users on the Xen system cause problems, or the server is restarted due to Xen related problems. This hasn't happened that often but you wouldn't currently run a system that needed 99.999% availability on a XEN virtual host if the system is vulnerable to a single server going down.
* You never know quite what your worst case performance is going to be like.
* If your system doesn't scale laterally (more servers) but only by buying a more powerful single server (some databases for example) then the Xen virtual hosting is not cost efficient.