Re: [Xen-users] I need help with fully utilizing xen on a new system

["Todd Deshane" <deshantm@xxxxxxxxx>]

On Thu, Jan 15, 2009 at 9:32 PM, Charles Derringer <charles@xxxxxxxxxxxxxxxx> wrote:

Hello xen list.  I am an absolute novice with Xen, having never been able to set it up despite my several trials.  I have built a new, modern system (last computer was seven years ago) with the hardware virtualization technologies so I'm hoping to be able to run Windows natively along side a graphical Linux desktop.

Consider the book "Running Xen" - http://runningxen.com

 

Here is what I was imagining ...

Dom0 = Gentoo
DomU = Gentoo w/gui
DomU = Ubuntu
DomU = Windows XP
DomU = Windows 2000
DomU = Windows 98
DomU = FreeBSD (multiple versions)

My hardware is dual quad core Xeon processors with 8 GB of RAM and several hard drives in a RAID 6 array.

Seems reasonable given the hardware and RAM

 

1) Is it better to have the "drives" that are exported to the DomUs be partitions, files, LVM, etc.?

This depends. There are some trade-offs. Performance vs. flexibility.

Image files giving the most flexibility, but with somewhat less performance.

Partitions/LVM/RAID more performance, but less flexibility.

You can mix and match based on your needs and there is a lot of questions and analysis on the list about this

search xen.markmail.org for more info and/or asked more specific questions.

 

2) If somebody has a computer running Xen and a Microsoft and Linux OS, how does one switch control between them?

Think of the computers as being on a local network. VNC, Remote Desktop, SSH, etc. all can work on the guests.

 

3) Does every component of the system need to be understood by the Dom0 to be able to be utilized by a DomU?

No, you can passthrough PCI devices directly to a domU. Doing this securely requires an IOMMU (Intel VT-d) or

a very recent AMD IOMMU. IOMMU is a chipset feature, it and VT-d have also been heavily discussed on this list.

There are some limitations without an IOMMU such as lack of support for a HVM/Full virt (i.e. Windows) guest to get

a PCI device passed to it 

 

4) If the Dom0 is x64, can a DomU be 32 bit?

Yes.

 

5) If the answer to 4 is yes, then can that DomU then be migrated to a Xen computer with a Dom0 that is 32 bit?

Probably. Haven't tried it myself, but others can probably confirm.

 

6) Does the Dom0 need to statically partition the resources (RAM, CPU) to the DomUs, or is there a dynamic, kernel / Xen controlled allocation that is possible?

The latest version of Xen support memory over commit, CPU over commit has been available for a long time.

 

Thanks for reading.  Let me know if I clarify anything.  I've tried to be vague because I do not really know much at all about Xen.  I don't know what's important to state or what is inconsequential  I've read the official "Xen 3.0 Documentation" PDF from xen.org, but I have a feeling that it is outdated, because I remember that being about the same as what I read years ago.

Xen is an open source project and sometimes the documentation is not the greatest. There is quite a bit of effort going into this, but it will be some time before it is considered good.

That being said, Xen is being used by a lot of people all over the world in production, companies, universities, researchers, etc. There is a lot of information on the

web (howtos, wiki information, etc. etc.) and quite a few books as well.

 

Hope that helps to get you started.

Cheers,

Todd

-- 
Todd Deshane
http://todddeshane.net
http://runningxen.com

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