libvirt users - Apr 2011 - kvm virtual server boot order

The boot order issue

   http://osdir.com/ml/libvir-list/2009-08/msg00398.html

resolved with the code changes specified by

   http://www.redhat.com/archives/libvir-list/2009-August/msg00340.html

seems to suggest that hard disks, cdroms, floppy devices (since they are
all disks) are ordered primarily by virtual bus type as encountered in the
domain xml.  This indicates that there can exist a conflict between the
primary and secondary boot device types.

Given the scenario where the disks of a virtual server are defined in the
following order

      harddisk hda
      harddisk vda
      cdrom vdb
      cdrom hdb

Boot device type is crdom.  Which cdrom device will be boot
attempted?
>From the above links, I'm guessing that hdb will be boot attempted. Is
this
the actual behavior?


Thanks,
Yee
--
yja at us.ibm.com   *   512-286-6793 T/L 363   *   Systems Management Software
Development   *   Austin, TX

> Given the scenario where the disks of a virtual server are defined in the
> following order
> 
>       harddisk hda
>       harddisk vda
>       cdrom vdb
>       cdrom hdb
> 
> Boot device type is crdom.  Which cdrom device will be boot attempted?
> >From the above links, I'm guessing that hdb will be boot attempted.
Is this
> the actual behavior?
That depends on BIOS implementation used by qemu and to be honest, I'm not
sure what the default behavior is; you would need to try that :-)

However, if you have new enough libvirt (>= 0.8.8), qemu and SeaBIOS (AFAIK
qemu >= 0.14.0 should be ok), you can better control boot order by using
per-device boot configuration. That is, instead of specifying

    <os>
      ...
      <boot dev='cdrom'/>
    </os>

you would use something like

    <devices>
      ...
      <disk type='file' device='cdrom'>
        ...
        <boot order='1'/>
      </disk>
    </devices>

It's also documented in libvirt XML documentation at
http://www.libvirt.org/formatdomain.html#elementsDisks

Jirka