Xen devel - Apr 2006 - vdb and vif connection errors

I hate intermittent problems ...

Most of the time, my domUs launch just fine.  But, occasionally I get a
failure to connect a vdb or vif and the domU fails to completely launch
("xm list" shows it is present but no console activity either through
"xm create -c" or through "xm console").   The log shows a
stack trace
in DevController.py in the area of waiting for hotplug response --
sometimes a timeout, sometimes an error.  There is usually no indication
in the main log or the hotplug log as to the ultimate cause.   Usually
the device is the first vdb in my disk array; but often it''s either
another of the vdb''s or a vif.

I sometimes find it''s something I did wrong like mistyping a vdb file
name, in which case I have no cause for complaint. 

However, sometimes the problem occurs for no apparent reason after
previous launches from the same domain configuration file.  

And, regardless of what causes the initial problem, once this failure
occurs I generally find that I cannot successfully launch any more domUs
until I reboot Xen/dom0.  BTW, I do try to make sure that the old,
failed domU is destroyed (as reported by xm list) before trying again.

So, some questions:

1. Is there something known to cause the seemingly random failures
(ones not caused by something I did wrong and generally not repeatable
after a reboot of Xen)?

2. Is something known to help avoid the launch failures in the first
place?

3. Are there places to look for problems other than xend and hotplug
logs?

4. Is there a way to clear things up without rebooting Xen?

Thanks for any advice -- or pointers to older discussions on this
point,

Colin Brown
Franklin University CIS

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Colin,

I''ve had this problem too.  I''ve noticed that if I destroy the
domU and
then mount the vdb through a loop back, access a file (not sure if this step
is necessary, but I do it), then unmount it, I''m able then to start the
domU.

As for your other questions, I have no idea.

Good luck,

Tony Hernandez
Rockwell Collins


On 4/7/06, Colin Brown <brownc@franklin.edu>
wrote:
>
> I hate intermittent problems ...
>
> Most of the time, my domUs launch just fine.  But, occasionally I get a
> failure to connect a vdb or vif and the domU fails to completely launch
> ("xm list" shows it is present but no console activity either
through
> "xm create -c" or through "xm console").   The log
shows a stack trace
> in DevController.py in the area of waiting for hotplug response --
> sometimes a timeout, sometimes an error.  There is usually no indication
> in the main log or the hotplug log as to the ultimate cause.   Usually
> the device is the first vdb in my disk array; but often it''s
either
> another of the vdb''s or a vif.
>
> I sometimes find it''s something I did wrong like mistyping a vdb
file
> name, in which case I have no cause for complaint.
>
> However, sometimes the problem occurs for no apparent reason after
> previous launches from the same domain configuration file.
>
> And, regardless of what causes the initial problem, once this failure
> occurs I generally find that I cannot successfully launch any more domUs
> until I reboot Xen/dom0.  BTW, I do try to make sure that the old,
> failed domU is destroyed (as reported by xm list) before trying again.
>
> So, some questions:
>
> 1. Is there something known to cause the seemingly random failures
> (ones not caused by something I did wrong and generally not repeatable
> after a reboot of Xen)?
>
> 2. Is something known to help avoid the launch failures in the first
> place?
>
> 3. Are there places to look for problems other than xend and hotplug
> logs?
>
> 4. Is there a way to clear things up without rebooting Xen?
>
> Thanks for any advice -- or pointers to older discussions on this
> point,
>
> Colin Brown
> Franklin University CIS
>
> _______________________________________________
> Xen-users mailing list
> Xen-users@lists.xensource.com
> http://lists.xensource.com/xen-users
>

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Xen-users mailing list
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Tony Hernandez wrote:
> Colin,
>  
> I''ve had this problem too.  I''ve noticed that if I
destroy the domU and
> then mount the vdb through a loop back, access a file (not sure if this 
> step is necessary, but I do it), then unmount it, I''m able then to
start
> the domU.
>  
> As for your other questions, I have no idea.
>  
> 
>  
> On 4/7/06, *Colin Brown* <brownc@franklin.edu 
> <mailto:brownc@franklin.edu>> wrote:
> 
>     I hate intermittent problems ...
> 
>     Most of the time, my domUs launch just fine.  But, occasionally I get a
>     failure to connect a vdb or vif and the domU fails to completely launch
>     ("xm list" shows it is present but no console activity either
through
>     "xm create -c" or through "xm console").   The log
shows a stack trace
>     in DevController.py in the area of waiting for hotplug response --
>     sometimes a timeout, sometimes an error.  There is usually no
indication
>     in the main log or the hotplug log as to the ultimate cause.   Usually
>     the device is the first vdb in my disk array; but often it''s
either
>     another of the vdb''s or a vif.
> 
>     I sometimes find it''s something I did wrong like mistyping a
vdb file
>     name, in which case I have no cause for complaint.
> 
This seems to be an old problem re-introduced in Xen 3.0.2.  I am 
experiencing it on my test server.  In my specific scenario sometimes a 
guest won''t start properly due to a vbd not "connecting"
properly.  It
occurs only when there is heavy access to xend.  Simply waiting until 
there are no other xm commands running lets the domains start-up.  At 
boot though even with the 5 second delay in starting domains some will 
exhibit this error.  On my side hotplug "cleans" itself and
I''m not
stuck with a paused domain, a simple xm create starts it right up.

Just a "me too".  I''m cross-posting this to xen-devel as I
know the
developers don''t actively monitor the xen-users list as closely.

Thanks,
Matt Ayres

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