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[Xen-users] Re: Some questions from a novice


  • To: Mark Williamson <mark.williamson@xxxxxxxxxxxx>
  • From: Zhiming Wu <zhiming.wu.atgm@xxxxxxxxx>
  • Date: Sun, 03 Feb 2008 14:25:26 +0800
  • Cc: xen-users@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Sat, 02 Feb 2008 22:26:08 -0800
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Hi Mark,

Thank you very much for you detailed explanation. Now I understand the situation and can decide what I should do.

Best Regards,
Zhiming Wu

Mark Williamson wrote:
Hello,

I am a novice at Xen and I have some questions about it and I will
deeply appreciate the answer from any of you.

Sure.

1. Can Xen be run on CPU that not support Virtualization Technology?
Because I have a Pentium M CPU that does not support VT.

Yes but you'll only be able to run Xen-aware (paravirtualised) guests. You can't run unmodified OSes such as Windows.

2. What is each variety of Xen kernel for? For example kernel-2.6-xen,
kernel-2.6-xen0 and kernel-2.6-xenU. Which one should be used for the
host OS? What are the differences between kernel-2.6-xen and
kernel-2.6-xen0?

2.6-xen0 is a kernel with dom0 functionality compiled in, with a fair number of device drivers built into the kernel (if I recall correctly) and not that many other driver built as modules.

2.6-xen also has dom0 functionality compiled in and it compiles a much larger set of modules to ensure compatibility with more hardware. This is probably a good choice for a dom0 kernel, as it'll support lots of devices by default.

2.6-xenU is a kernel that does not include dom0 functionality, so it can only run in an unprivileged domain. You can use this as the kernel in your guest VMs.

You can use a dom0-aware kernel (2.6-xen or 2.6-xen0) in *any* domain, including an unprivileged domain. It is safe to use a dom0-aware kernel in an unprivileged domain, it won't be able to do any harm.

A 2.6-xenU build is just slightly smaller because it doesn't include dom0 functionality - that's the only difference.

3. I have to build the customer Xen kernel to support some special
device, can a newer version, such as 2.6.23.9 used in my system now, of
linux kernel be used?

Not really, no.

You can't build 2.6.23 from kernel.org to run as a dom0 *at all*, so you won't be able to use that to get better device support. You can run 2.6.23 as a domU kernel, although the support is better tested and more complete if you use the XenLinux kernel from XenSource, at the moment.

If you use a distro with good Xen support, such as Fedora or CentOS then it will include a distro-patched XenLinux kernel with extra driver support, etc. Fedora ports the Xen patches to work with newer versions of Linux. If you want a more stable, server OS, then you could try CentOS. CentOS 5 uses the 2.6.18 kernel but other drivers are backported to enhance its hardware support.

There are other distros that do similar modifications, so you might find you have luck with one of those instead. Fedora and CentOS are just the ones I know most about ;-)

Cheers,
Mark



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