Re: [Xen-users] Error: ... Backend device not found.

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> I can't create a domU. This following error I get. Once it seemed that
> domU was started because xm list was showing etch03 running but xm
> console etch03 points to an error and etch03 crashed.
>
> server1:/vd# xm create -c etch03.cfg
> Using config file "/etc/xen/etch03.cfg".
> Error: Device 771 (vbd) could not be connected. Backend device not found.
>
> ---
> title           Xen 3.0.3-1-i386 / Debian GNU/Linux, kernel
> 2.6.18-5-xen-686 root            (hd0,0)
> kernel          /xen-3.0.3-1-i386-pae.gz
> module          /vmlinuz-2.6.18-5-xen-686 root=/dev/md1 ro xencons=off
> console=tty0
> module          /initrd.img-2.6.18-5-xen-686
> savedefault
> ---
>
> ...
> kernel = "/boot/vmlinuz-2.6.18-5-xen-686"
> ramdisk = "/boot/initrd.img-2.6.18-5-xen-686"
>
> disk = ['file:/vd/etch03.vd,hda3,w','file:/vd/etch03.sd,hda2,w']
> ...

Are you sure that both these files exist at the path you've stated?

> 2.
> I'm also not sure if I should use xen-3.0.3-1-i386.gz instead of
> xen-3.0.3-1-i386-pae.gz, but xen-3.0.3-1-i386-pae.gz boots the dom0 and
> xen-3.0.3-1-i386.gz does'nt. The maschine has only 512 MB RAM so I think
> its not nessesary to use xen-3.0.3-1-i386-pae.gz. Does it makes a big
> differens to use xen-3.0.3-1-i386-pae.gz instead of xen-3.0.3-1-i386.gz
> if this case?

The PAE setting of Xen needs to match the PAE setting of the dom0 kernel.  If 
they're not matched, then dom0 will not boot.

PAE may have a slight performance and memory usage penalty, but I doubt it 
would be significant.  The performance difference may not even be measurable 
for your workloads.  The memory usage difference should not be very big (the 
pagetables are bigger under PAE so they take up more space).

An advantage of using PAE is that RedHat seem to have standardised on it for 
their Xenified kernels, so it would make it easier to run Fedora and RHEL 
domUs.  Some of the other Xen OS ports (e.g. NetBSD, Plan 9) don't run on 
PAE, although you could still always install them using HVM mode.

Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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