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

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] "xm save" hanging when saving domain in "pause" state
From: Tomas Kouba <tomas@xxxxxxxx>
Date: Tue, 18 Jul 2006 13:24:15 +0200
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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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