[Fedora-xen] Getting Fedora yum-installed domU running on fedora with fedora-xen packages

[Daniel P. Berrange]

On Tue, Dec 19, 2006 at 12:06:42PM +0100, Henning Sprang wrote:
> Hi Tom,
> 
> On 12/18/06, Tom Horsley <tomhorsley at adelphia.net> wrote:
> >[...]
> >Not on my system at work. We installed a 32 bit hvm FC6 on a physical
> >disk via virt-manager, and it worked fine under x86_64 dom0 (also
> >FC6). I did manage to screw it up somehow trying to get the kernel
> >updated, but it was working great before that :-).
> 
> Seems I did not explain correctly what I meant.
> 
> With what you do, HVM Installs take place exactly not into partitions
> you defined from the outside, but into a block devices, and the hvm
> system then does full partitioning inside this.

Paravirt installs should work in the same way - you are mapping through
virtual disks, not virtual partitions. The latter just happens to work
by chance, and is not supported.

> What I mean what fedora kernels have problems with is when pointing
> the disk config directly onto a partition created from outside the
> domU.

Try mapping your disk through as 'xvda' instead of 'hda1'.

> An example:
> 
> In your setup you probably have a disk config line like this;
> 
> disk=[ 'phy:/dev/hdb1,hda,w']
> 
> What I mean is a setup that look like this:
> 
> disk = [ 'phy:/dev/hdb1,hda1,w']

Two issues there

1. We strongly recommend *against* specifying  hdX / sdX for virtual disk 
   device type in paravirt guests. The Xen XVD driver is hijacking the 
   IDE / SCSI drivers to do this hack. This will not be accepted upstream
   and so support will likely disappear in a future kernel-xen release.
   Use xvdX  instead, eg

     'phy:/dev/hdb1,xvda,w'

2. The first form of disk config you have is the preferred setup. ie
   map the partition from Dom0, through to DomU as a *disk*, not a
   partition. DomU should then partition this further as required,
   Your second config 'phy:/dev/hdb1,xvda1,w' may /happen/ to work, but
   there are no guarentees this will continue to work in the future.
   Only the 'phy:/dev/hdb1,xvda,w' format is supported for compatability
   long term.

    eg, /dev/hdb1 in Dom0, maps to /dev/xvda in DomU
        then DomU  can create /dev/xvda1 as needed

   By having nested partition tables in this way, you ensure that Dom0
   does not see the individual partitions from the DomU. If it were
   to see the indiivdual DomU partitions, and say both Dom0 and DomU
   have a partition formated ext3 with same label, then mount by label
   in Dom0 may end up picking up DomU's partition by accident.
   In addition tools in DomU may well get confuse by seeing 'xdva1'
   without a corresponding 'xvda'.
   

Regards,
Dan.
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