An Introduction to Virtualization
by Liz van Dijk on October 28, 2008 2:00 AM EST- Posted in
- IT Computing
When Are Hypervisors a Good Solution?
As much as these companies' publicity campaigns might be trying to sell their products off as the only solution you'll ever need, we are here to give you an objective view of where they are useful.
Hypervisors are a great solution for situations where hardware vastly outperforms the software's needs. Using a "bare metal" hypervisor, every VM is able to make use of the hardware, without being influenced by the others. For a company looking to consolidate a number of varying servers (mixing for example Windows systems with Linux-based systems), using a hypervisor would be the logical step. The big downside of this technology is that each virtual machine needs to run a full operating system to support itself, making the collective resources spent on running these operating systems a rather large bite out of the hardware's total pool.
Windows and OS X living peacefully together; it's all possible with software hypervisors…
This also seems to be the main problem when using a software-based hypervisor. While this platform does succeed perfectly in offering most of the VM's guest OS functionality, in performance-based environments the cost of running an extra OS on top of an existing one can make the entire solution a bit bloated for constant use. Nonetheless, the ability to run a completely sand-boxed environment has caused many developers to use hypervisors as their software's playgrounds. Much in the same way, since Apple made the switch to Intel-based hardware, software hypervisors have allowed users of OS X to virtualize a Windows system without actually having to set up a multi-boot system. This goes a long way in proving that they are a very solid solution when actual functionality is more important than raw performance.
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Ralphik - Wednesday, October 29, 2008 - link
Hello everybody,I have installed a virtual Win98 on my computer, which is running WinXP. The problem I have is that there are no GeForce7 and higher drivers available for such old Windows platforms - has anyone got a tip or a cracked driver that I could use? It now has a completely useless S3 Virge driver installed . . .
Jovec - Friday, October 31, 2008 - link
Unless I'm missing something (new), your Win98 running in your VM will not see your GeForce video card, or indeed any of the actual hardware in your computer. It just sees the virtual hardware provided by your VM software - typically an emulated basic VGA video adapter and AC'97 sound. VM software emulates an emulates an entire virtual computer on your host PC, but does not use the physical hardware natively.In short, you are not going to get Geforce level graphics power in your Win98 VM.
stmok - Wednesday, October 29, 2008 - link
"Could it be that these two pieces of software are using related techniques for their 3D acceleration? Stay tuned, as we will definitely be looking into this in further research!"=> Parallels took Wine's 3D acceleration component. More specifically, they took the translator that allowed one to translate OpenGL calls to DirectX and vice versa.
There was a minor issue about this when Parallels are not compliant with the open source license of Wine. But that was settled when Parallels complied with the LGPL two weeks later.
=> http://parallelsvirtualization.blogspot.com/2007/0...">http://parallelsvirtualization.blogspot...2007/07/...
=> http://en.wikipedia.org/wiki/Parallels_Desktop_for...">http://en.wikipedia.org/wiki/Parallels_Desktop_for...
What annoys me, is that they never bothered with adding 3D Acceleration support in the Linux version of Parallels. The only option is the very current release of VMware Workstation. (Version 6.5 has technology implemented from their VMware Fusion product).
duploxxx - Tuesday, October 28, 2008 - link
btw is this a teaser for the long announced virtualization performance review?Vidmo - Tuesday, October 28, 2008 - link
I was hoping this article would get into some of the latest hardware technologies designed for better virtualization. It's still quite confusing trying to determine which hardware platforms and CPUs support VT-d for example.The article is a nice software overview, but seems incomplete without getting into the hardware side of the issues.
solusstultus - Tuesday, October 28, 2008 - link
Hardware support for VT is not used by most/any? commercial hypervisors (VMware doesn't use it) and has been shown to actually have lower performance in many cases than binary translation:http://www.vmware.com/pdf/asplos235_adams.pdf">http://www.vmware.com/pdf/asplos235_adams.pdf
duploxxx - Tuesday, October 28, 2008 - link
unfortunately your link is 2 years old.Current statement for Vmware ESX is that you should use the hardware virtualization layer when you have 64bit OS at any time and when virtualization layer 2 aka NPT from amd (ept when intel launches nehalem next year) at any time.
solusstultus - Wednesday, October 29, 2008 - link
While I don't claim to be an expert, that's the most recent study that I have seen that actually lists performance results from both techniques.If you have seen more recent results, do you have a link? I would be interested in reading it.
From what I have seen, NPT addresses overheads associated with switching from the Guest to the VMM during page table updates (which can occur frequently when using small pages). However, the other main source of overhead cited in the paper that I referenced were traps into the VMMs on system calls which could be replaced by less expensive direct links to VMM routines in translated code. So unless the newer hardware support virtualization implementations address this (they might, I haven't looked at the documentation), it seems translation could still be potentially faster for some apps, and that an ideal implementation would make use of both in different situations.
Vidmo - Tuesday, October 28, 2008 - link
Ahh I somehow missed the link to your hardware article.http://it.anandtech.com/IT/showdoc.aspx?i=3263&...">http://it.anandtech.com/IT/showdoc.aspx?i=3263&...
Very well done. Would it be possible to update that article to reflect VT-d and possibly TV-i technologies as well?
LizVD - Tuesday, October 28, 2008 - link
Thanks for the input!The real purpose of this article was to provide a "beginner-safe" intro into the things we have been discussing on Anandtech IT for the past couple of months, so in-depth discussion of each of the technologies is something we avoided on purpose, to keep focus on the basic differences without getting carried away.
Your question is an interesting one, however, and of the sort we'd like to properly address in our blogs, so keep an eye on them, as we'll be looking into it.