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Date: Fri, 14 Feb 2014 16:09:02 +0100
From: Stefan Hajnoczi <stefanha@gmail.com>
Message-ID: <20140214150902.GN17391@stefanha-thinkpad.redhat.com>
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Subject: Re: [Qemu-devel] qemu-1.7.0 vm migration with nbd usage
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To: xuanmao_001 <xuanmao_001@163.com>
Cc: qemu-devel <qemu-devel@nongnu.org>, qemu-discuss <qemu-discuss@nongnu.org>

On Wed, Feb 12, 2014 at 04:35:19PM +0800, xuanmao_001 wrote:
> Hi, Is there a document describe vm migration with nbd server or any example about it?

NBD supports migration because it is a network storage protocol.

Imagine you have a "source" host and a "destination" host.  The source
host is currently running the guest.  The destination host is the live
migration target.

There is also an NBD server host that is independent of the source and
destination hosts.

Launch QEMU on the destination host with the same command-line as the
source host, but append "-incoming tcp::1234".

Start live migration using the "migrate" command in the QEMU monitor on
the source host.  Live migration will run until it completes.

Finally, you should see your VM has migrated to the destination host.
Disk I/O will still use the NBD server host.

So there's nothing really special here.  NBD is just considered shared
storage.

Stefan