Checkpointing

On Thu, Jun 29, 2006 at 05:14:11PM -0600, Chris Vaughan
wrote:
> So what's the difference between a "Live
Migration" & "Save" then?  Does the
> live migration keep the image open and the save does
not?  To me they seam
> to be 2 peas in a pod but I guess I'm mistaken.

Live migration ensures that the filesystem is passed as is
from one
state to the other. Restoring a checkpointed system would
mean that
the system would suddenly warp back in time wrt to the
filesystem, or
what is effectively the same from the system's POV the
filesystem
suddenly warped ahead in time.

For example: Perhaps your crash between the checkpointing
and the
resuming was caused by rm -fr / and no checkpointing could
undo that 

So checkpointing in xen would only work hand in hand with
block device
snapshoting.

> Thanks
> 
> 
> On 6/29/06, Daniel Veillard <veillardredhat.com> wrote:
> >
> >On Thu, Jun 29, 2006 at 04:56:21PM -0600, Chris
Vaughan wrote:
> >> Hi,
> >>
> >> Is there any way you can save a xen domain
without suspending it or
> >stopping
> >> it?  I want to set up something so if my xen
session crashes I can fire
> >up
> >> another xen session from the save file that I
created 5 minutes before
> >the
> >> crash and hopefully minimize downtime.
> >
> >  Doesn't work in general because you would have
to save the state of the
> >filesystems too. Xen operations don't allow a save
and continue for that
> >reason I was told.
> >
> >Daniel
> >
> 
> 
> 



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Chris Vaughan wrote:
> So what's the difference between a "Live
Migration" & "Save" then?  Does
> the live migration keep the image open and the save
does not?  To me
> they seam to be 2 peas in a pod but I guess I'm
mistaken.
> 
> Thanks
> 
> 

Migration saves VM state and assumes that the filesystem
does not
change.  Checkpointing would have to restore the filesystem
to the same
point in time that the snapshot was taken of the VM. 
Perhaps you could
swing it with CoW or something, but it doesn't work now.

-- 
Christopher G. Stach II

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