Re: [Xen-users] "xm save" hanging when saving domain in "pause" state

[Tomas Kouba <tomas@xxxxxxxx>]

Petersson, Mats wrote:
>     ------------------------------------------------------------------------
>     *From:* xen-users-bounces@xxxxxxxxxxxxxxxxxxx
>     [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] *On Behalf Of *Claris
>     Castillo
>     *Sent:* 15 July 2006 00:12
>     *To:* xen-users@xxxxxxxxxxxxxxxxxxx
>     *Subject:* Re: [Xen-users] "xm save" hanging when saving domain in
>     "pause" state
>
>     Thanks for your reply Michael. These are bad news... I am actually
>     looking at options to do offline migration, that is, take snapshots
>     of the VMs state and their corresponding filesystems in order to be
>     able to fire them up in a different host if for some reason the
>     original host they are assigned to crashes at some point. I have
>     found some threads with *very* similar questions in some mailing
>     lists, unfortunately they don't extend to more than two entries
>     and have more questions than answers.
>      
>      
>
>     Ok. Parameter of design? As far as I understand by "pausing" a
>     domain, XEN is basically indicating the scheduler not to
>     give any other slice to that particular VM from that point in time
>     (until the VM is unpaused)  Why can't XEN0 just surpass the
>     scheduler, indicate to the VM that it must disconnect its devices
>     (basically doing an enhanced version of "xm unpause") and put itself
>     in quiescent state, and wait to be notified by the VM (step 2 in
>     your email)?. What is wrong with such approach? Am I missing
>     something? Would not this enable a clean checkpointing procedure?
>
>     Thanks
>
>     cc 
>      
>
> cc, I think you could do exactly what you want with JUST xm save, it 
> automatically "pauses" the domain. Is there any particular reason you 
> CAN'T do that? Why do you need to do xm pause before xm save?
I think this is because when paused you can do lvm snapshot and so you will 
be sure that lvm snapshot and saved vm are from the same moment.
From my point of view the approach you suggest cannot ensure that. Or am I 
missing something?
--
Tomas Kouba

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