This is a known issue.
It has been fixed in xen unstable.
The problem is loop device is not leased after the guest destroyed.
If execute "losetup -d /dev/loopX" in domain0, the problem will be solved
temporarily.
>-----Original Message-----
>From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
>[mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Thomas Karsten
>Sent: 2006年7月20日 17:26
>To: xen-users@xxxxxxxxxxxxxxxxxxx
>Subject: Re: [Xen-users] Error: Device 769 (vbd) could not be connected...Limit
>of 25 domains.
>
>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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