Xen users - Mar 2008 - conversion between Full-virtualization and Para-virtualization

Hi,All,

I installed a guest os with full-virtualization and a local volume as the disk,
now becuase of poor performance,
I want to change the full-virtualization guest to para-virtualization,
so I just changed the config file to boot the guest os with para-virtualization,
but it fails to boot.
but how can I convert the full-virtualization guest to para-virtualization
without reinstall the os,on other hands,can I convert a para-virtualization to
full-virtualization in xen?
are there any suggestion?many thanks!


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There are several things you need to check.  First, I''m going to assume
you''re running Linux as your guest O/S.  If this is not the case,
please respond with the O/S and version you''re using.  If you are using
Linux, check the following:
1) In your guest config file on dom0, you need to switch your disk devices from
IDE to xvd*.  So, if you have a line that specifies a local volume as hda in
your config file, change this to xvda.  hdb -> xvdb, etc.
2) You need to specify the correct root device in your config file for the domU.
This is done with root= in the file.  If your previous root device was hda1,
your root line would say root="/dev/xvda1 ro" or something similar.
3) You need to make sure that the kernel either has the Xen virtual block device
module built in or that you create an initrd for your guest with this module. 
You also need to transfer the kernel and initrd into your dom0 so that you can
put the kernel= and ramdisk= lines in your config file.
4) Finally, you need to change /etc/fstab to point to your new root device, e.g.
/dev/xvda1.
 
It would also be really helpful if you''d post the error you''re
getting.  Just telling us that, "it fails to boot" isn''t very
descriptive.
 
-Nick
>>> On 2008/03/18 at 10:39, "HA" <jiecho@sina.com>
wrote:
Hi,All,
 
I installed a guest os with full-virtualization and a local volume as the disk,
now becuase of poor performance,
I want to change the full-virtualization guest to para-virtualization,
so I just changed the config file to boot the guest os with para-virtualization,
but it fails to boot.
but how can I convert the full-virtualization guest to para-virtualization
without reinstall the os,on other hands,can I convert a para-virtualization to
full-virtualization in xen?
are there any suggestion?many thanks!
 


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Nick Couchman wrote:
> There are several things you need to check.  First, I''m going to 
> assume you''re running Linux as your guest O/S.  If this is not the
> case, please respond with the O/S and version you''re using.  If
you
> are using Linux, check the following:
> 1) In your guest config file on dom0, you need to switch your disk 
> devices from IDE to xvd*.  So, if you have a line that specifies a 
> local volume as hda in your config file, change this to xvda.  hdb -> 
> xvdb, etc.
> 2) You need to specify the correct root device in your config file for 
> the domU.  This is done with root= in the file.  If your previous root 
> device was hda1, your root line would say root="/dev/xvda1 ro" or
> something similar.
In theory, you can also use the pygrub boot loader. In practice, I''ve 
had a bit of trouble with RHEL and Fedora installers getting grub to 
operate in the virtualized environment from the installation CD''s
rescue
mode. I''ve no idea how they did it with anaconda: but you can use the 
approach described above with the para-virtualized kernel installed in 
Dom0 to get it up and running, and run grub inside the operating domain 
to get it to work.

Note that building an initrd in Dom0 for this stunt, or getting grub 
fully configured with an initrd inside the DomU, may take a bit of work 
as well.



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