Xen users - Jan 2006 - Error: Device 769 (vbd) could not be connected. Backend device not found.

Hi, 

I have installed debian 3.1 on an Intel Pentium D processor 920 ( including 
vanderpool.)

The installation worked fine and i''m able to start guest-domains.

When I try to start the 5.th Guest-Domain, I Get the following error:


Error: Device 769 (vbd) could not be connected. Backend device not found.

this problem exists still if i have shutdown or destroyed all guests, after 
this I can start 4 guests again.

could someone help me ?

thank you
stephan


-- 
Stephan Augustin
Rosenpark 3
65795 Hattersheim
06190/9355448
0173/1735867

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Stephan Augustin wrote:
> When I try to start the 5.th Guest-Domain, I Get the following error:
>
> Error: Device 769 (vbd) could not be connected. Backend device not found.
Seems a lot of people are having this problem.
Should be in the FAQ, and the error message should be clearer.

I have no clue where or how to fix the error message, however.

I can take a wild guess at why you might be seeing it though - have
you run out of loop devices in dom0?

HTH

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I also see this with the disks mounted as LVM partitions and not using 
loopbacks.  It happens for me off the first or second DomU instance, 
seemingly at random.

Sorry I have no info on a fix though; just thought I''d feed in my 
experience that''s not related to loopback devices.

Tony

On 31/01/2006, at 5:23 AM, Molle Bestefich wrote:
> Stephan Augustin wrote:
>> When I try to start the 5.th Guest-Domain, I Get the following error:
>>
>> Error: Device 769 (vbd) could not be connected. Backend device not 
>> found.
>
> Seems a lot of people are having this problem.
> Should be in the FAQ, and the error message should be clearer.
>
> I have no clue where or how to fix the error message, however.
>
> I can take a wild guess at why you might be seeing it though - have
> you run out of loop devices in dom0?
>
> HTH
>
> _______________________________________________
> Xen-users mailing list
> Xen-users@lists.xensource.com
> http://lists.xensource.com/xen-users
>
tony clark
director - tony.clark@rsp.com.au
---------------------------------------------------------------
rising sun pictures - www.rsp.com.au
redefining visual effects delivery
---------------------------------------------------------------
address	level 1 / 133 gouger street
		adelaide south australia 5000
---------------------------------------------------------------  
adelaide ph +61 8 8400 6400 fax +61 8 8400 6401
sydney    ph +61 2 9338 6400 fax +61 2 9338 6401
---------------------------------------------------------------
rising sun research - http://research.rsp.com.au
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Hi, 
I tried some times again, and now i am running 7 machines concurrent.
during installation, the same error occured, but this was because i
hadn''t
mounted the image-file partition at this time.
the only difference i can see is that i now didnt use the dom0_mem=64000 
parameter in the grub/menu.lst config.

perhaps it was this , I dont know.
if someone knows more about, please tell me

thank you for your fast help

stephan


Am Montag, 30. Januar 2006 21:01 schrieb Tony Clark:
> I also see this with the disks mounted as LVM partitions and not using
> loopbacks.  It happens for me off the first or second DomU instance,
> seemingly at random.
>
> Sorry I have no info on a fix though; just thought I''d feed in my
> experience that''s not related to loopback devices.
>
> Tony
>
> On 31/01/2006, at 5:23 AM, Molle Bestefich wrote:
> > Stephan Augustin wrote:
> >> When I try to start the 5.th Guest-Domain, I Get the following
error:
> >>
> >> Error: Device 769 (vbd) could not be connected. Backend device not
> >> found.
> >
> > Seems a lot of people are having this problem.
> > Should be in the FAQ, and the error message should be clearer.
> >
> > I have no clue where or how to fix the error message, however.
> >
> > I can take a wild guess at why you might be seeing it though - have
> > you run out of loop devices in dom0?
> >
> > HTH
> >
> > _______________________________________________
> > Xen-users mailing list
> > Xen-users@lists.xensource.com
> > http://lists.xensource.com/xen-users
>
> tony clark
> director - tony.clark@rsp.com.au
> ---------------------------------------------------------------
> rising sun pictures - www.rsp.com.au
> redefining visual effects delivery
> ---------------------------------------------------------------
> address	level 1 / 133 gouger street
> 		adelaide south australia 5000
> ---------------------------------------------------------------  
> adelaide ph +61 8 8400 6400 fax +61 8 8400 6401
> sydney    ph +61 2 9338 6400 fax +61 2 9338 6401
> ---------------------------------------------------------------
> rising sun research - http://research.rsp.com.au
> ---------------------------------------------------------------
-- 
Stephan Augustin
Rosenpark 3
65795 Hattersheim
06190/9355448
0173/1735867

_______________________________________________
Xen-users mailing list
Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users

I have figured out that if it happens all loop-devices are fully used. can i 
get more of them ?

stephan

Am Montag, 30. Januar 2006 21:01 schrieb Tony Clark:
> I also see this with the disks mounted as LVM partitions and not using
> loopbacks.  It happens for me off the first or second DomU instance,
> seemingly at random.
>
> Sorry I have no info on a fix though; just thought I''d feed in my
> experience that''s not related to loopback devices.
>
> Tony
>
> On 31/01/2006, at 5:23 AM, Molle Bestefich wrote:
> > Stephan Augustin wrote:
> >> When I try to start the 5.th Guest-Domain, I Get the following
error:
> >>
> >> Error: Device 769 (vbd) could not be connected. Backend device not
> >> found.
> >
> > Seems a lot of people are having this problem.
> > Should be in the FAQ, and the error message should be clearer.
> >
> > I have no clue where or how to fix the error message, however.
> >
> > I can take a wild guess at why you might be seeing it though - have
> > you run out of loop devices in dom0?
> >
> > HTH
> >
> > _______________________________________________
> > Xen-users mailing list
> > Xen-users@lists.xensource.com
> > http://lists.xensource.com/xen-users
>
> tony clark
> director - tony.clark@rsp.com.au
> ---------------------------------------------------------------
> rising sun pictures - www.rsp.com.au
> redefining visual effects delivery
> ---------------------------------------------------------------
> address	level 1 / 133 gouger street
> 		adelaide south australia 5000
> ---------------------------------------------------------------  
> adelaide ph +61 8 8400 6400 fax +61 8 8400 6401
> sydney    ph +61 2 9338 6400 fax +61 2 9338 6401
> ---------------------------------------------------------------
> rising sun research - http://research.rsp.com.au
> ---------------------------------------------------------------
-- 
Stephan Augustin
Rosenpark 3
65795 Hattersheim
06190/9355448
0173/1735867

_______________________________________________
Xen-users mailing list
Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users

On Tuesday 31 January 2006 09:14, Stephan Augustin
wrote:
> I have figured out that if it happens all loop-devices are fully used. can
> i get more of them ?
AFAIK you can set the number of loopback devices in your kernel config. Thus 
you have to recompile your xen-kernel.

Michael
-- 
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Thinking Objects Software GmbH    |   mailto: michael.mey@to.com 
Lilienthalstrasse 2/1             |   phone: +49 711 88770-147
70825 Stuttgart-Korntal, Germany  |   fax: +49 711 88770-449
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Michael Mey wrote:
> Stephan Augustin wrote:
> > I have figured out that if it happens all loop-devices are fully used.
can
> > i get more of them ?
>
> AFAIK you can set the number of loopback devices in your kernel config.
Thus
> you have to recompile your xen-kernel.
That may be true, but it''s much easier to adjust it on the kernel
command line.
Just add max_loop=128 or some such.

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Am Dienstag, 31. Januar 2006 13:32 schrieb Molle
Bestefich:
> Michael Mey wrote:
> > Stephan Augustin wrote:
> > > I have figured out that if it happens all loop-devices are fully
used.
> > > can i get more of them ?
> >
> > AFAIK you can set the number of loopback devices in your kernel
config.
> > Thus you have to recompile your xen-kernel.
>
> That may be true, but it''s much easier to adjust it on the kernel
command
> line. Just add max_loop=128 or some such.
Do you mean the commandline 
kernel /boot/xen.gz
in /boot/grub/menu.lst ?

stephan

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Stephan Augustin wrote:
> > That may be true, but it''s much easier to adjust it on the
kernel command
> > line. Just add max_loop=128 or some such.
>
> Do you mean the commandline
> kernel /boot/xen.gz
> in /boot/grub/menu.lst ?
No, that''s the parameter line for the hypervisor.
The loop devices exist within the domain 0 kernel.
So you must append the max_loop parameter to the
"module=<linux-dom0-kernel>" line in your grub configuration
file.

Sorry, should''ve mentioned that.

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Am Dienstag, 31. Januar 2006 14:20 schrieb Molle
Bestefich:
> Stephan Augustin wrote:
> > > That may be true, but it''s much easier to adjust it on
the kernel
> > > command line. Just add max_loop=128 or some such.
> >
> > Do you mean the commandline
> > kernel /boot/xen.gz
> > in /boot/grub/menu.lst ?
>
> No, that''s the parameter line for the hypervisor.
> The loop devices exist within the domain 0 kernel.
> So you must append the max_loop parameter to the
> "module=<linux-dom0-kernel>" line in your grub
configuration file.
>
> Sorry, should''ve mentioned that.
Sorry , but this doesnt work for me..
do I have to do something else for get this working ?

i have this script :

"If you have the “loop” driver compiled into your kernel, you need to add 
“max_loop=64” to your kernel boot arguments (the “append=” line in lilo.conf, 
or to the end of the “kernel” line in grub’s menu.lst), and reboot."


If you have the “loop” driver compiled as a module, you need to insmod it with 
“max_loop=64” added to its options. On Debian systems, you 
edit /etc/modules.conf and add “options loop max_loop=64”, and “rmmod loop” 
“modprobe loop”.

If you’re using devfs, then stop here. The new /dev/loop* will appear 
automatically. If not, you’ll need to edit and run MAKEDEV:
Change:

        loop)
                for part in 0 1 2 3 4 5 6 7
                do
                        makedev loop$part b 7 $part $disk
                done
                ;;

To:

        loop)
                for part in `seq 0 63`
                do
                        makedev loop$part b 7 $part $disk
                done
                ;;

And run “MAKEDEV loop”.
"

with the original debian -kernel, It is possible to use the modules - but this 
doesnt create more loop-devices.
and even the kernel /boot/vmlinuz-2.6[...] max_loop=64 
line does not work.

under the xen-kernel the command-line doesnt work ( I dont get more devices) , 
and the modprobe command aborts with an error


stephan


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Stephan Augustin wrote:
[...]
Hrm, good info.
In a more concise form it would be appropriate for a XEN FAQ, me thinks.
> and even the
> kernel /boot/vmlinuz-2.6[...] max_loop=64
> line does not work.
Doesn''t look right either.
Dom0 is loaded via the "module", not the "kernel" grub
command.
> under the xen-kernel the command-line doesnt work ( I dont get more
devices) ,
As in,
 "they do not appear in /dev" or
 "I''ve run ''mknod /dev/loop/123 b 7 123'' but
I''m getting error
messages when I use the device
?

In case of the latter, which error messages?
> and the modprobe command aborts with an error
Provide a better error description, please.
The above doesn''t really get us anywhere.

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Am Dienstag, 31. Januar 2006 14:52 schrieb Molle
Bestefich:
> Stephan Augustin wrote:
> [...]
> Hrm, good info.
> In a more concise form it would be appropriate for a XEN FAQ, me thinks.
>
> > and even the
> > kernel /boot/vmlinuz-2.6[...] max_loop=64
> > line does not work.
>
> Doesn''t look right either.
> Dom0 is loaded via the "module", not the "kernel" grub
command.
^^ this was the command line for the unmodified original debian kernel without 
xen, for showing that it dont works in original debian ( without xen ! ) 
> > under the xen-kernel the command-line doesnt work ( I dont get more
> > devices) ,
> As in,
>  "they do not appear in /dev" or
>  "I''ve run ''mknod /dev/loop/123 b 7 123''
but I''m getting error
> messages when I use the device
> ?
I realised the ^^ snipped patch in the MAKEDEV file, which should create the 
loop-devices between 0 up to 63 during boot

They do not appear in /dev

I''ve run mknod /dev/loop8 b 7 8 but I didn''t get any error
message
vhost:~# losetup /dev/loop8
/dev/loop8: [f5d8]:-1 (l:�
                          $) offset -1208435526, undefined encryption
loop: can''t get info on device /dev/loop8: No such device or address
now i run xm create debian.5
now it works :-? I dont know why...
but why are these devices not createt automatically on boot ?

but it Works - Thank you very much for your help

stephan


> In case of the latter, which error messages?
>
> > and the modprobe command aborts with an error
>
> Provide a better error description, please.
> The above doesn''t really get us anywhere.
>
> _______________________________________________
> Xen-users mailing list
> Xen-users@lists.xensource.com
> http://lists.xensource.com/xen-users
-- 
Stephan Augustin
Rosenpark 3
65795 Hattersheim
06190/9355448
0173/1735867

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Stephan Augustin wrote:
> but why are these devices not createt automatically on boot ?
Depends on whether you are using a static /dev, devfs or udev.
> but it Works - Thank you very much for your help
np.

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