RE: [Xen-users] Xen a couple of questions

["Petersson, Mats" <Mats.Petersson@xxxxxxx>]

> No, I think the issue is that CentOS is pegged to RedHat's kernel 
> release model, where an RHEL deployment is supposed to be stable and 
> consistent throughout the lifespan of the operating system.  For 
> reliable behavior in such an environment, your DomU *must* 
> have a kernel 
> as similar as posible to that deployed by RedHat. Dom0 can be 
> forced to 
> be more recent to get critical features (shoving Xen Dom0 
> into a 2.6.9 
> kernel is just asking for pain, though.) So Dom0 pretty much needed a 
> much newer kernel.

The default kernel build in current Xen releases (since 3.0.4 or before)
is to build one kernel that works for both. Yes, there are some
differences between a XenU and Xen0 config, in that one has the
"privileged" option set, and there are some differences in drivers added
to the kernel (particularly, XenU doesn't normally have ANY support for
ANY hardware drivers). But you should ALWAYS be able to sue the Dom0
kernel for DomU, even if the other way around doesn't necessarily hold
true. 


> 
> Notice that for RHEL and CentOS 4.5, which now can gracefully be 
> installed as DomU's on top of a 5.0 Dom0, they only have kernel-xenU 
> packages, not kernel-xen packages. If you want a 4.5 machine 
> as a Dom0, 
> you need to use the xensource kernel or roll your own. And do 
> *not* try 
> to backport virt-manager to CentOS 4.5 without being prepared 
> for a lot 
> of pain.
> 
> There's also the issue of kernel size: when you're doing 
> micro-deployments (stripped down DomU's for firewall or similar mini 
> setups) there are some advantages to teeny-tiny kernels, and 
> since you 
> have a consistent environment of necessary hardware drivers, you can 
> actually do it. But it's a pain to support, and it also lets anyone 
> doing a "uname -a" find out that you're in a Xen guest environment.

Yes, if you are loading dozens or more of guest kernels, the size of the
actual kernel will matter. I'm not sure how much the difference is tho'.


--
Mats
> 
> So there are tradeoffs.
> 
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> 
> 
> 



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