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Date: Tue, 5 Nov 2013 14:34:12 +0100
From: Stefan Hajnoczi <stefanha@gmail.com>
Message-ID: <20131105133412.GD16457@stefanha-thinkpad.redhat.com>
References: <D3E216785288A145B7BC975F83A2ED1043EEDBB3@szxeml556-mbx.china.huawei.com>
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Subject: Re: [Qemu-devel] [migration] questions about removing the old
 block-migration code
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To: "Zhanghaoyu (A)" <haoyu.zhang@huawei.com>
Cc: "Huangweidong (C)" <weidong.huang@huawei.com>, "Michael S. Tsirkin" <mst@redhat.com>, Michal Privoznik <mprivozn@redhat.com>, Linqiangmin <linqiangmin@huawei.com>, Marcelo Tosatti <mtosatti@redhat.com>, "paolo.bonzini@gmail.com" <paolo.bonzini@gmail.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, Xiahai <xiahai@huawei.com>, "quintela@redhat.com" <quintela@redhat.com>, Zanghongyong <zanghongyong@huawei.com>, Luonengjun <luonengjun@huawei.com>, "Huangpeng (Peter)" <peter.huangpeng@huawei.com>

On Sun, Nov 03, 2013 at 04:01:36AM +0000, Zhanghaoyu (A) wrote:
> I read below words on the report of <KVM Live Migration: Weather forecast (May 29, 2013)>,
> We were going to remove the old block-migration code
> Then people fixed it
> Good: it works now
> Bad: We have to maintain both
> It uses the same port than migration
> You need to migrate all/none of block devices
> 
> The old block-migration code said above is that in block-migration.c?

Yes.

> What are the reasons of removing the old block-migration code? Buggy implementation? Or need to migrate all/none of block devices?

Buggy and tightly coupled with the live migration code, making it hard
to modify either area independently.

> What's the substitutional method? drive_mirror?

drive_mirror over NBD is an alternative.  There are security and
integration challenges with those approaches but libvirt has added
drive-mirror block migration support.

Stefan