Re: [Xen-users] Error: Device 769 (vbd) could not be connected... Limit of 25 domains.

[Thomas Karsten <thomas@xxxxxxxxxxx>]

Hi,

I used the Debian GNU/Linux Etch system on the Xen 3.0 Live CD (Version 
1.0) to have a look where I am doing some mistake in my system's 
configuration. I used the standard config file '/root/deb-conf' and 
launched the following command:

# for ((i=100; i < 140; i++)); do xm create /root/deb-conf
name=guestdom$i; done

This time I was able to create up to 15 guest domains, all the others 
resulted in the following error message:

Device 2049 (vbd) could not be connected. Backend device not found.

(As far as I experienced, the device 2049 is /dev/sda1.)

However, I would like to know, if some of you also run into this problem, 
when launching this command on the same system (Xen 3.0 Live CD). I 
tested this on another machine, where I could only create up to 7 
concurrent guest domains.

Is the problem that I face related to the hardware? Or is it only related 
to the software (i.e. configuration of the whole system)? In latter case, 
why does the Live CD behave different on different computers? Or am I 
missing an important point in the configuration process?

I am very curious about this problem and how to solve it, since it has 
been a topic on this mailing list many times, but I did not see any 
solution posted.

I hope somebody can try to launch this command using that Xen Live CD and 
tell me about the results.

Thank you very much,
Thomas

On Wednesday 19 July 2006 18:18, Thomas Karsten wrote:
> Hello,
>
> I am running Xen 3.0.2 in an Ubuntu 6.06 Linux system (kernel
> 2.6.16-xen). Xend is running and works well.
>
> I would like to use Xen to run about 80 domains (for testing purpose).
> All domains share the same image file (which therefor is mounted
> 'readonly' by Xen) and each domain is configured to use only 10 MB of
> RAM. I am using a script to generate name, hostname and IP address for
> each guest (it simply loops over i and calls:'xm create name=guestdom$i
> hostname=$i ip=192.168.1. $i').
>
> Everything works fine, but after 25 concurrent running domains Xen
> refuses to create any further domains, giving me the error:
>
> Error: Device 769 (vbd) could not be connected. Hotplug scripts not
> working.
>
> On this mailing list I found several threads dealing with this error
> message. However, I did not find that anybody is facing this kind of
> limitation that I have. For your information, the number of loopback
> devices in my system is 132. Also, I am not running out of memory, this
> would be stated by Xen (I have 1500 MB of RAM, where 500 MB are
> occupied by Xen).
>
> I can remove a guest domain and create a new one, this is no problem.
> However, on my system I am not able to create more than 25 domains at
> the same time. Can anybody help please?
>
> Thank you very much, all ideas are appreciated,
> Thomas

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