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Date: Tue, 24 Jul 2012 07:12:25 -0400 (EDT)
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH V4 0/3] Block migration if any of the block
 device is busy
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To: Kevin Wolf <kwolf@redhat.com>
Cc: Stefan Hajnoczi <stefanha@gmail.com>, benoit canet <benoit.canet@gmail.com>, =?utf-8?Q?Beno=C3=AEt?= Canet <benoit@irqsave.net>, qemu-devel@nongnu.org, stefanha@linux.vnet.ibm.com


> > Hmm...maybe this is a policy decision.  I figure if you are running
> > image streaming and try to migrate, chances are you're migration
> > will break on the destination host because you were trying to do
> > pre-copy storage migration and never finished.

Streaming is post-copy, and can be interrupted every time you want.

Mirroring is pre-copy.  That's another story, but even then the way
to "emulate" migrate -b/-i (and make it much more efficient, as you can
see from the last few patches I just posted) is exactly to run mirroring
in parallel to RAM migration.  This is relatively difficult to do by hand
(though I'd like to improve it in 1.3 if only to get rid of block-migration.c)
and requires giving the user a considerable amount of rope, but it is doable.

So, thinking about it a bit more, this patch looks like a good idea in principle,
but actually it is counterproductive.

Paolo